The Cellular Basis of Reproduction and Inheritance

The Cellular Basis of Reproduction and Inheritance
Chapter 8 The Cellular Basis of Reproduction and Inheritance Lecture by Richard L. Myers Translated by Nabih A. Baeshen 1

CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION
Copyright © 2009 Pearson Education, Inc. 2

8.1 Like begets like, more or less
Living organisms reproduce by two methods Asexual reproduction Offspring are identical to the original cell or organism Involves inheritance of all genes from one parent Sexual reproduction Offspring are similar to parents, but show variations in traits Involves inheritance of unique sets of genes from two parents Most eukaryotic organisms are capable of both asexual and sexual reproduction. Students may be surprised to learn that asexual reproduction plays a major role in the life cycles of many organisms. For example, the unicellular algae Chlamydomonas generates an increased population by asexual reproduction when conditions are favorable for cell division. In unfavorable conditions, the organism undergoes sexual reproduction. This has the advantage of producing a new combination of genes and traits that could be advantageous for survival under new environmental conditions. Student Misconceptions and Concerns 1. As the authors note in Module 8.1, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused. 2. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated. Teaching Tips 1. Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like? Copyright © 2009 Pearson Education, Inc. 3

8.3 Prokaryotes reproduce by binary fission
Binary fission means “dividing in half” Occurs in prokaryotic cells Two identical cells arise from one cell Steps in the process: A single circular chromosome duplicates, and the copies begin to separate from each other The cell elongates, and the chromosomal copies separate further The plasma membrane grows inward at the midpoint to divide the cells The process of binary fission is very rapid. E. coli cells divide every 20 minutes under optimal environmental conditions. The antibiotic penicillin inhibits the growth of the bacterial cell wall. Cells can duplicate their internal contents, including the chromosome, but will burst when they become too large for the existing cell wall. Student Misconceptions and Concerns 1. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated. Teaching Tips Consider contrasting the timing of DNA replication and cytokinesis in prokaryotes and eukaryotes. In prokaryotes, addressed in Module 8.3, these processes are over-lapping. However, as revealed in the next few modules, these events are separate in eukaryotes. Copyright © 2009 Pearson Education, Inc. 4

Binary fission of a prokaryotic cell
Plasma membrane Prokaryotic chromosome Cell wall Duplication of chromosome and separation of copies 1 Binary fission of a prokaryotic cell Continued elongation of theا cell and movement of copies 2 Figure 8.3A Binary fission of a prokaryotic cell. This figure shows the steps in binary fission. Division into two daughter cells 3 5

THE EUKARYOTIC CELL CYCLE AND MITOSIS

8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division
Eukaryotic chromosomes are composed of chromatin Chromatin = DNA + proteins To prepare for division, the chromatin becomes highly compact, and the chromosomes are visible with a microscope Early in the division process, chromosomes duplicate Each chromosome appears as two sister chromatids, containing identical DNA molecules Sister chromatids are joined at the centromere, a narrow region Chromatin is compacted about 100,000 fold to produce the interphase/metaphase chromosome. If all the DNA in the human chromosomes were aligned, it would stretch for one meter. All of this DNA is condensed to fit into a nucleus that can only be seen with the aid of a microscope. The centromere has a unique DNA sequence involving repeated stretches of nucleotides. In biotechnological applications, artificial chromosomes can be produced that have a centromeric sequence. This chromosome will be properly distributed during cell division because the spindle fibers attach to the artificial centromeric sequence. Student Misconceptions and Concerns 1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic when discussing DNA replication. 2. Students are often confused by photographs of chromosomes. Such photographs, such as Figure 8.4B, typically show duplicated chromosomes during some aspect of cell division. It remains unclear to many why (a) chromosome structure is typically different between interphase G1 and the stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes duplicate. Teaching Tips 1. Figure 8.4C is an important point of reference for some basic terminology. Consider referring to it as you distinguish between a DNA molecule and a chromosome, unreplicated and replicated chromosomes, and the nature of sister chromatids. Copyright © 2009 Pearson Education, Inc. 7

Chromosome duplication of a duplicated chromosome
Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Electron micrograph of a duplicated chromosome Sister chromatids and distribution Figure 8.4C Chromosome duplication and distribution. The term chromatid is used to describe duplicates that are connected at the centromere. This diagram emphasizes that the structures are called chromosomes when separated. This leads to a brief time when a cell has double the number of chromosomes, as in anaphase and telophase of mitosis, prior to cytokinesis. 8

8.5 The cell cycle multiplies cells
The cell cycle is an ordered sequence of events for cell division It consists of two stages INTERPHASE Interphase: duplication of cell contents G1: growth, increase in cytoplasm S: duplication of chromosomes G2: growth, preparation for division - Mitotic phase: divisiMitosis: division of the nucleus Cytokinesis: division of cytoplasm S (DNA synthesis) G1 Cytokinesis G2 Mitosis Differences in the length of the cell cycle can be instructive. Yeast cells have a 2-hour life cycle, while human cells in culture take about 24 hours to divide. Mitosis and cytokinesis represent a shorter section of the cycle, lasting one hour for cultured human cells. Teaching Tips 1.The authors note in Module 8.5 that each of your students consists of about 100 trillion cells. It is likely that this number is beyond comprehension for most of your students. Consider sharing several simple examples of the enormity of that number to try to make it more meaningful. For example, the U.S. population in 2008 is about 310 million people. To give every one of those people about $323,000, we will need a total of $100 trillion. Here is another example. If we give you $31,688 every second of your life, and you lived for 100 years, you would receive $100 trillion dollars. 2.The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (1) a chromosome before DNA replication and (2) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids. We have doubled the DNA, but the molecules remain attached (although not attached in the same way as the wire). You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes. 3. In G1, the chromosomes have not duplicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle. MITOTIC PHASE (M) The eukaryotic cell cycle Copyright © 2009 Pearson Education, Inc. 9

8.6 Cell division is a continuum of dynamic changes
Mitosis progresses through a series of stages Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis often overlaps telophase Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc. 10

A mitotic spindle is required to divide the chromosomes The mitotic spindle is composed of microtubules It is produced by centrosomes, structures in the cytoplasm that: Organize microtubule arrangement Contain a pair of centrioles in animal cells The role of centrioles in cell division is unclear Centrioles give rise to basal bodies that are the foundations for cilia and flagella. They are found in animal cells but also in plants such as mosses and ferns that have swimming sperm. They are not found in flowering plants, showing that centrioles are not essential for spindle formation. There is other evidence, however, that suggests centrioles may influence progression through alternative stages in the cell cycle, including entry into the S phase and completion of cytokinesis. (Reviewed in A. W. Murray, 2001, “Centrioles at the Checkpoint,” Science, 291:1499–1501.) For the BioFlix Animation Mitosis, go to Animation and Video Files. Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc. 11

(with centriole pairs) Chromosome, consisting of two sister chromatids
INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin Early mitotic spindle Centrosome Fragments of Nuclear envelope Kinetochore ة Figure 8.6 The stages of cell division. Nuclear Envelope Plasma Membrane Centromere Spindle Microtubules Nucleolus ال Chromosome, consisting of two sister chromatids 12

Interphase In the cytoplasm Cytoplasmic contents double Two centrosomes form In the nucleus Chromosomes duplicate during the S phase Nucleoli, sites of ribosome assembly, are visible Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc. 13

TELOPHASE AND CYTOKINESIS
ANAPHASE TELOPHASE AND CYTOKINESIS METAPHASE Metaphase plate Cleavage furrow ا Nucleolus Forming Figure 8.6 The stages of cell division. Nuclear envelope Forming Spindle Daughter chromosomes 14

8.7 Cytokinesis differs for plant and animal cells
Cytokinesis Cleavage in animal cells A cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin The cleavage furrow deepens to separate the contents into two cells Cytokinesis in plant cells A cell plate forms in the middle from vesicles containing cell wall material The cell plate grows outward to reach the edges, dividing the contents into two cells Each cell has a plasma membrane and cell wall This material allows a review of cellular components. Students can be reminded that microtubules are composed of actin molecules and that actin and myosin work in concert for muscle cell contraction. They can also be reminded that vesicles have a lipid boundary that will contribute to the plasma membrane of the new plant cells. For the BLAST Animation Cytokinesis in Plants, go to Animation and Video Files. Teaching Tips 1. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). This occurs in human development during the formation of the placenta. 2. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this association. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because, like the drawstring just beneath the surface of the sweat pants, the microfilaments are just beneath the surface of the cell’s plasma membrane. Copyright © 2009 Pearson Education, Inc. 15

Cleavage furrow Contracting ring of Microfilaments ة Daughter cells
Figure 8.7A Cleavage of an animal cell. Daughter cells 16

Growth (in an onion root)
Figure 8.11A Growth (in an onion root). Growth (in an onion root) )

Mitosis Telophase Early Anaphase Midi Anaphase prophaseى Late Anaphase
Metaphase Early Anaphase Midi Anaphase Late Anaphase prophaseى Telophase

MEIOSIS AND CROSSING OVER

8.12 Chromosomes are matched in homologous pairs
Somatic cells have pairs of homologous chromosomes, receiving one member of each pair from each parent Length Centromere position Gene locations A locus (plural, loci) is the position of a gene Different versions of a gene may be found at the same locus on maternal and paternal chromosomes Student Misconceptions and Concerns 1. Some students might conclude that sex chromosomes function only in determining the sex of the individual. As the authors note, sex chromosomes contain genes not involved in sex determination. Teaching Tips 1. Students might recall some basic genetics, remembering that for many traits a person receives a separate “signal” from mom and dad. These separate signals for the same trait are carried on the same portion of homologous chromosomes, such as the freckle trait discussed in Module 8.12. 2. Consider helping students through mitosis and meiosis by developing an analogy to pairs of shoes. In this case, any given species has a certain number of pairs of shoes, or homologous chromosomes. 3. In the shoe analogy, females have 23 pairs of matching shoes, while males have 22 matching pairs and 1 odd pair Maybe a sandal and a sneaker! Copyright © 2009 Pearson Education, Inc. 20

8.12 Chromosomes are matched in homologous pairs
Homologous pair ofchromosomes The human sex chromosomes X and Y differ in size and genetic composition Pairs of autosomes have the same size and genetic composition Centromere Applying Your Knowledge Humans have 46 chromosomes; how many homologous pairs does that represent? 23 If there is one pair of sex chromosomes, how many pairs of autosomes are found in humans? 22 Student Misconceptions and Concerns 1. Some students might conclude that sex chromosomes function only in determining the sex of the individual. As the authors note, sex chromosomes contain genes not involved in sex determination. Teaching Tips 1. Students might recall some basic genetics, remembering that for many traits a person receives a separate “signal” from mom and dad. These separate signals for the same trait are carried on the same portion of homologous chromosomes, such as the freckle trait discussed in Module 8.12. 2. Consider helping students through mitosis and meiosis by developing an analogy to pairs of shoes. In this case, any given species has a certain number of pairs of shoes, or homologous chromosomes. 3. In the shoe analogy, females have 23 pairs of matching shoes, while males have 22 matching pairs and 1 odd pair Maybe a sandal and a sneaker! Sister chromatids One duplicated chromosome A homologous pair of chromosomes 21

8.13 Gametes have a single set of chromosomes
Meiosis is a process that converts diploid nuclei to haploid nuclei Diploid cells have two homologous sets of chromosomes “ Haploid cells have one set of chromosomes Meiosis occurs in the sex organs, producing gametes—sperm and eggs Fertilization is the union of sperm and egg The zygote has a diploid chromosome number, one set from each parent Teaching Tips 1. You might want to get your students thinking by asking them why eggs and sperm are different. (This depends upon the species, but within vertebrates, eggs, and sperm are specialized for different tasks. Sperm are adapted to move to an egg and donate a nucleus. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and growth.) 22

8.14 Meiosis reduces the chromosome number from diploid to haploid
Like mitosis, meiosis is preceded by interphase Chromosomes duplicate during the S phase Unlike mitosis, meiosis has two divisions During meiosis I, homologous chromosomes separate The chromosome number is reduced by half During meiosis II, sister chromatids separate The chromosome number remains the same Student Misconceptions and Concerns 1. Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. 2. How meiosis results in four haploid cells, yet mitosis yields two diploid cells, is often memorized but seldom understood. It can be explained like this. Consider a pair of chromosomes in a cell before any cell divisions. This pair of chromosomes duplicates such that two chromosomes become four (although each pair of sister chromatids are joined at their centromeres). Therefore, mitosis and meiosis each typically begin with four chromosomes. Mitosis divides once, producing two cells, each with two chromosomes. Meiosis divides twice, sorting the four chromosomes into four separate cells. Teaching Tips 1. In meiosis I and meiosis II, the processes begin with duplicated pairs of chromosomes. This pair becomes two pairs. The two pairs include four items. Sort this group into two subgroups, and you are back to two pairs. Divide again, and you have separated four items into four groups of one. This can work with the shoe analogy if you wish to continue the reference. A pair of shoes is “reproduced” and becomes two pairs. Mitosis sorts them back into two pairs of shoes. However, meiosis keeps sorting, eventually isolating each shoe. Each solitary shoe would then represent a gamete, which would then be matched with another similar shoe (gamete) to make a new pair of shoes (organism). 23

8.14 Meiosis reduces the chromosome number from diploid to haploid
Events in the nucleus during meiosis I Prophase I Chromosomes coil and become compact Homologous chromosomes come together as pairs by synapsis Each pair, with four chromatids, is called a tetrad Nonsister chromatids exchange genetic material by crossing over Sister chromatids are exact duplicates, but nonsister chromatids belong to different members of the homologous pair. Any one of the maternal chromatids is a nonsister to any of the paternal chromatids. Since maternal and paternal chromatids can have different versions of genes (alleles) at corresponding loci, crossing over potentially produces new genetic combinations, mixing maternal and paternal versions on the same chromatid. Student Misconceptions and Concerns 1. Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling is prevented if each gamete has only half the genetic material of the adult cells. 2. How meiosis results in four haploid cells, yet mitosis yields two diploid cells, is often memorized but seldom understood. It can be explained like this. Consider a pair of chromosomes in a cell before any cell divisions. This pair of chromosomes duplicates such that two chromosomes become four (although each pair of sister chromatids are joined at their centromeres). Therefore, mitosis and meiosis each typically begin with four chromosomes. Mitosis divides once, producing two cells, each with two chromosomes. Meiosis divides twice, sorting the four chromosomes into four separate cells. Teaching Tips 1. In meiosis I and meiosis II, the processes begin with duplicated pairs of chromosomes. This pair becomes two pairs. The two pairs include four items. Sort this group into two subgroups, and you are back to two pairs. Divide again, and you have separated four items into four groups of one. This can work with the shoe analogy if you wish to continue the reference. A pair of shoes is “reproduced” and becomes two pairs. Mitosis sorts them back into two pairs of shoes. However, meiosis keeps sorting, eventually isolating each shoe. Each solitary shoe would then represent a gamete, which would then be matched with another similar shoe (gamete) to make a new pair of shoes (organism). 24

The stages of miosis I MEIOSIS I: Homologous chromosomes separate
الانقسام الاختزالي الأول: انفصال الأزواج الكروموزمومية المتماثلة INTERPHASE الطور البيني PROPHASE I الطور التمهيدي الأول METAPHASE I الطور الاستوائي الأول ANAPHASE I الطور الانفصالي الأول Centrosomes (with Centriole pairs) ) Sites of crossing over Microtubules attached to Kinetochore Metaphase Plate Sister chromatids remain attached Spindle Figure 8.14 The stages of meiosis. Nuclear Envelope Sister Chromatids Tetrad Centromere (with kinetochore) Chromatin Homologous chromosomes separate The stages of miosis I 25

MEIOSIS II: Sister chromatids separate الانقسام الاختزالي الثاني: انفصال الكروماتيدات الشقيقة TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Cleavage furrow Sister chromatids Separate Haploid daughter cells forming Figure 8.14 The stages of meiosis. The stages of miosis II 26

MEIOSIS A B C D E F I G H PROPHASE I METAPHASE I ANAPHASE I
ANAPHASE II TELOPHASE II TETRAD D E F G H I PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II TETRAD

Chapter 9 Patterns Lecture by Richard L. Myers
Patterns Lecture by Richard L. Myers Translated by Nabih A. Baeshen 28

9.1 The science of genetics has ancient roots
Pangenesis was an early explanation for inheritance It was proposed by Hippocrates Particles called pangenes came from all parts of the organism to be incorporated into eggs or sperm Characteristics acquired during the parents’ lifetime could be transferred to the offspring Aristotle rejected pangenesis and argued that instead of particles, the potential to produce the traits was inherited Blending was another idea, based on plant breeding Hereditary material from parents mixes together to form an intermediate trait, like mixing paint Ask students to give examples that contradict these early proposals. Most will agree that if something happens to a parent during his/her lifetime, the children do not inherit the change, as suggested by this real-life example: A man who lost part of his thumb in an accident became the father of five children, each with fully formed thumbs. Skin color may appear as a blended trait, since children of dark- and light-skinned parents are often intermediate between the two. However, two parents with intermediate skin color can have children with darker or lighter skin than either parent. (See Module 9.14.) In England, there was a recent report of two parents with medium skin color having twin daughters, one with light skin and the other with dark skin. Teaching Tips 1. As you begin your lectures on genetics, consider challenging your students to explain why the theories of pangenesis and blending are incorrect. Perhaps just pick one of the two. You might even ask for short responses from everyone at the start of class or as an assignment before the first lectures. In addition to arousing interest in the answers, the responses should reveal the diverse backgrounds of your students entering this discussion and reveal any preexisting confusion on the subject of genetics. 2. The concept of pangenesis is analogous to the structure of United States representation in Congress. Each congressional district sends a congressman or congresswoman (pangene) to the U.S. House of Representatives (gamete). There, all parts of the United States (body) are represented. 3. In this or future lectures addressing evolution, you may mention that pangenesis is a mechanism that permits Lamarckian evolution. Copyright © 2009 Pearson Education, Inc.

9.2 Experimental genetics began in an abbey garden
Gregor Mendel discovered principles of genetics in experiments with the garden pea Mendel showed that parents pass heritable factors to offspring (heritable factors are now called genes) Advantages of using pea plants Controlled matings Self-fertilization or cross-fertilization Observable characteristics with two distinct forms True-breeding strain Student Misconceptions and Concerns 1. The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet, Mendel’s selection of pea plant traits typically showed complete dominance, rather than the possibility for such gradual inheritance. Teaching Tips 1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. Copyright © 2009 Pearson Education, Inc.

The seven pea characteristics studied by Mendel
Flower color White Axial Purple Flower position Terminal Yellow Seed color Green Round Seed shape Wrinkled Inflated Pod shape Constricted Pod color Tall Stem length Dwarf Character Dominant Trait Recessive Trait The seven pea characteristics studied by Mendel Figure 9.2D The seven pea characters studied by Mendel. Mendel studied seven characteristics for pea plants. Later studies have shown that pea plants have seven pairs of chromosomes, and each of these characteristics is on a different chromosome. This explains why Mendel’s results were not affected by genetic recombination. 32

Example of a monohybrid cross
9.3 Mendel’s law of segregation describes the inheritance of a single character Example of a monohybrid cross Parental generation: purple flowers  white flowers F1 generation: all plants with purple flowers F2 generation: of plants with purple flowers of plants with white flowers Mendel needed to explain Why one trait seemed to disappear in the F1 generation Why that trait reappeared in one quarter of the F2 offspring For the BLAST Animation Single-Trait Crosses, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios. Teaching Tips 1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 2. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP pp and (b) Pp pp. 3. For students struggling with basic terminology, an analogy between a genetic trait and a pair of shoes might be helpful. A person might wear a pair of shoes in which both shoes match (homozygous), or less likely, a person might wear shoes that do not match (heterozygous). 4. Another analogy that might help struggling students is a pair of people trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. This (heterozygous) couple eats at home (the dominant allele “wins”). 5. Figure 9.4 can be of great benefit when introducing genetic terminology of genes. For students struggling to think abstractly, such a visual aid may be essential when describing these features in lecture. Copyright © 2009 Pearson Education, Inc. 33

Crosses tracking one character (flower color)
F2 generationية Fertilization among F1 plants (F1 ´ F1) ¾ of plants have purple flowers ¼ of plants have white flowers F1 generation All plants have purple flowers Purple flowers White flowers P generation (true-breeding ( parents) Crosses tracking one character (flower color) Figure 9.3A Crosses tracking one character (flower color). 34

Genetic makeup (alleles) Explanation of the crosses in previous figure
P plants 1 – 2 Genotypic ratio 1 PP : 2 Pp : 1 pp Phenotypic ratio 3 purple : 1 white F1 plants (hybrids) Gametes Genetic makeup (alleles) All All Pp Sperm Eggs البيض PP p pp Pp P F2 plants Explanation of the crosses in previous figure Figure 9.3B Explanation of the crosses in Figure 9.3A. A Punnett square is used to show all possible fertilization events for parental gametes. In three quarters of the F2 genotypes, there will be at least one dominant allele.

Matching gene loci on homologous chromosomes
Homozygous for the dominant allele Dominant allele recessive allele Heterozygous Recessive allele Genotype: P B a PP aa b Bb Matching gene loci on homologous chromosomes Figure 9.4 Matching gene loci on homologous chromosomes. 36

9.8 CONNECTION: Genetic traits in humans can be tracked through family pedigrees
A pedigree Shows the inheritance of a trait in a family through multiple generations Demonstrates dominant or recessive inheritance Can also be used to deduce genotypes of family members Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in the lecture. Teaching Tips 1. Students also seem to learn much from Figure 9.8b by analyzing the possible genotypes for the people whose complete genotype is not known. Consider challenging your students to suggest the possible genotypes for these people. Copyright © 2009 Pearson Education, Inc.

Examples of single-gene inherited traits in humans
Freckles Widow’s peak No freckles Straight hairline Dominant Traits Recessive Traits Examples of single-gene inherited traits in humans Free earlobe Attached earlobe Figure 9.8A Examples of single-gene inherited traits in humans. This figure shows three traits that are determined by single genes with alternate alleles. The role of the dominant allele in influencing the phenotype when at least one copy is present can be emphasized here.

Examples of single-gene inherited traits in humans
Free earlobe Attached earlobe FF or Ff ff Genotype Phenotype Examples of single-gene inherited traits in humans Dominant Traits Recessive Traits Figure 9.8A Examples of single-gene inherited traits in humans.

Ff Ff ff Ff FF ff ff Ff Ff ff or Ff ff FF or Ff
First generation (grandparents) ) Ff Ff ff Ff Second generation (parents, aunts, and uncles) FF ff ff Ff Ff ff or Ff Third generation (two sisters) ) ff FF or Female أ Male Figure 9.8B Pedigree showing inheritance of attached versus free earlobe in a hypothetical family. Ff Affected “ Unaffected Pedigree showing inheritance of attached versus free earlobe in a hypothetical family

Parents Normal Dd ي Normal Dd Dd DD Eggs Offspring Dd dd
Parents Normal Dd ي Normal Dd Sperm D d Dd Normal (carrier) “ DD Normal D Eggs Offspring Figure 9.9A Offspring produced by parents who are both carriers for a recessive disorder. This diagram shows the inheritance of deafness, a recessive trait, from two heterozygous parents. Dd Normal (carrier) ط “ dd Deaf d Offspring produced by parents who are both carriers for a recessive diorder

VARIATIONS ON MENDEL’S LAWS

9.11 Incomplete dominance results in intermediate phenotypes
Incomplete dominance Neither allele is dominant over the other Expression of both alleles is observed as an intermediate phenotype in the heterozygous individual Student Misconceptions and Concerns 1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from this simplistic model of inheritance. 2. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 3. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a gray shade. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to instructors, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you can catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. Copyright © 2009 Pearson Education, Inc. 43

Incomplete dominance in snapdragon color
P generation 1 – 2 F1 generation F2 generation Red RR Gametes Eggs Sperm rR Rr rr R r Pink White Incomplete dominance in snapdragon color Figure 9.11A Incomplete dominance in snapdragon color. This figure shows incomplete dominance in flower color. The difference in color between the RR and Rr genotypes is proposed to be a dosage effect, where the presence of one allele allows the production of half as much pigment as the presence of two alleles. 44

9.20 Chromosomes determine sex in many species
X-Y system in mammals, fruit flies XX = female; XY = male XX = أ ; XY = X-O system in grasshoppers and roaches XX = female; XO = male XX = ; XO = Z-W in system in birds, butterflies, and some fishes ZW = female, ZZ = male ZW= ZZ = Chromosome number in ants and bees Diploid = female; haploid = male While fruit flies have X and Y chromosomes, sex determination is influenced by the X chromosome to autosome ratio. Females with XX genotype have two X chromosomes and two sets of autosomes for an X:A ratio of 1. Males with XY genotype have one X chromosome and two sets of autosomes for an X:A ratio of 0.5. Teaching Tips 1. In certain animals, such as crocodilians and many turtles, sex is not genetically determined. Instead, the incubation temperature of the eggs determines an animal’s sex. Students may enjoy researching this unique form of sex determination, often identified as TSD (temperature-dependent sex determination). 45

(male) (\) (female) (أ\) 44 + XY XX 22 X Y
(male) (\) Sperm حيوانات منوية (female) (أ\) 44 + XY Parents’ diploid cells \\ XX 22 X Y Egg ب\ Offspring (diploid) \\) X-Y system \ Figure 9.20B The X-Y system. 46

Chromosome number system
22 + X XX X-O system X-O 76 ZZ ZW Z-W system Z-W 16 Chromosome number system 32 Figure 9.20C The X-O system. 47

Molecular Biology of the Gene
Chapter 10 Molecular Biology of the Gene Lecture by Richard L. Myers Translated by Nabih A. Baeshen

MOLECULAR STRUCTURE OF THE GENETIC MATERIAL
Copyright © 2009 Pearson Education, Inc.

10.2 DNA and RNA are polymers of nucleotides
The monomer unit of DNA and RNA is the nucleotide, containing 5-carbon sugar Phosphate group Nitrogenous base A sugar-phosphate backbone is formed by covalent bonding between the phosphate of one nucleotide and the sugar of the next nucleotide Nitrogenous bases extend from the sugar-phosphate backbone Student Misconceptions and Concerns 1. If your class has not yet studied Chapter 3, consider assigning module 3.16 on “Nucleic Acids” before addressing the contents of Chapter 10. 2. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips 1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Griffith, Hershey, Chase, Franklin, and Chargaff). 2. Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars. Copyright © 2009 Pearson Education, Inc.

Sugar-phosphate backbone The structure of DNA polynucleotide
Sugar-phosphate backbone Phosphate group Nitrogenous base Sugar ر Nitrogenous base (A, G, C, or T) DNA nucleotide Phosphate group Thymine (T) ال (T) Figure 10.2A The structure of a DNA polynucleotide. This figure shows a short stretch of DNA. The nucleotides can theoretically be arranged in any order, since all nucleotides have a phosphate group that can be joined to the sugar of any other nucleotide. The order of nucleotides within a gene, however, is what provides the information for producing a specific protein. Sugar (deoxyribose) ) DNA nucleotide DNA polynucleotide The structure of DNA polynucleotide

10.3 DNA is a double-stranded helix
DNA is composed of two polynucleotide chains joined together by hydrogen bonding between bases, twisted into a helical shape The sugar-phosphate backbone is on the outside The nitrogenous bases are perpendicular to the backbone in the interior Specific pairs of bases give the helix a uniform shape A pairs with T, forming two hydrogen bonds G pairs with C, forming three hydrogen bonds The specific nature of the base-pairing interactions not only accounted for the uniform diameter of the double helix but also conformed to the chemical characteristics of the nucleotide bases and chemical composition studies of DNA. RNA molecules have secondary structure that involves hydrogen bonding between bases on the same polynucleotide chain. Thus the structure will be unique to RNA of a specific sequence. The covalent bonding between nucleotides can be contrasted with the hydrogen bonding between bases. Although individual hydrogen bonds are weaker than covalent bonds, the large number of hydrogen bonds along a double helical DNA molecule stabilizes the helix. Hydrogen bonds can be temporarily disrupted so that the DNA strands separate, but each individual strand remains intact. Student Misconceptions and Concerns 1. If your class has not yet studied Chapter 3, consider assigning module 3.16 on “Nucleic Acids” before addressing the contents of Chapter 10. 2. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips 1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Griffith, Hershey, Chase, Franklin, and Chargaff). 2. The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to explain what the parts of the ladder represent. The wooden rungs represent pairs of nitrogenous bases joined together by hydrogen bonds. Each rope represents a sugar-phosphate backbone. Copyright © 2009 Pearson Education, Inc.

Partial chemical structure Three presentations of DNA
Hydrogen bond Base pair Figure 10.3D Three representations of DNA. Hydrogen bonding between bases can be seen in the partial chemical structure in the center. This figure can also be used to point out the opposite polarity of the DNA chains as emphasized in Module From top to bottom, the chain on the left is oriented 5  3 while the chain on the right is oriented 3  5. A 5 end has a free phosphate group attached to the 5 carbon of the sugar and a 3 end has a free –OH group attached to the 3 carbon of the sugar. Ribbon model Partial chemical structure Computer model Three presentations of DNA

Nucleosomes are formed when DNA is wrapped around histone proteins
11.3 DNA packing in eukaryotic chromosomes helps regulate gene expression Eukaryotic chromosomes undergo multiple levels of folding and coiling, called DNA packing Nucleosomes are formed when DNA is wrapped around histone proteins “Beads on a string” appearance Each bead includes DNA plus 8 histone molecules String is the linker DNA that connects nucleosomes Tight helical fiber is a coiling of the nucleosome string Supercoil is a coiling of the tight helical fiber Metaphase chromosome represents the highest level of packing DNA packing can prevent transcription Student Misconceptions and Concerns 1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. 2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation. Teaching Tips 1. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away. 2. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression. Copyright © 2009 Pearson Education, Inc.

DNA packing in a eukaryotic chromosome
11.3 DNA packing in eukaryotic chromosomes helps regulate gene expression DNA double helix (2-nm diameter) “Beads on a string” Linker Histones Metaphase Chromosome Tight helical fiber (30-nm diameter) Nucleosome (10-nm diameter) Supercoil (300-nm diameter) 700 nm Figure 11.3 DNA packing in a eukaryotic chromosome. This figure shows the increasing levels of DNA packing. The initial level of the nucleosome involves ~140 base pairs of DNA surrounding 8 molecules of histone proteins. A linker region of 40–60 nucleotides is found between nucleosomes. Histones are highly evolutionarily conserved proteins, with only two amino acid changes between histone H4 molecules in pea plants and cows. The combination of histones with DNA has long been associated with the inhibition of transcription. Histones have sites for acetylation in their amino-terminal regions that can reduce binding between positively charged lysine residues and negatively charged DNA. Histone acetylation has been correlated with increased transcriptional activity as it would allow for transient removal of the histone-protein portion of the nucleosome during transcription. DNA packing in a eukaryotic chromosome

10.4 DNA replication depends on specific base pairing
DNA replication follows a semiconservative model The two DNA strands separate Each strand is used as a pattern to produce a complementary strand, using specific base pairing Each new DNA helix has one old strand with one new strand Student Misconceptions and Concerns 1. The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips 1. Demonstrate the complementary base pairing within DNA. Present students with the base sequence to one side of a DNA molecule and have them work quickly at their seats to determine the sequence of the complimentary strand. For some students, these sorts of quick practice are necessary to reinforce a concept and break up a lecture. 2. The authors note that the semiconservative model of DNA replication is like making a photo from a negative and then a new negative from the photo. In each new negative and photo pair, the new item was made from an old item. Copyright © 2009 Pearson Education, Inc.

A template mode for DNA replication
Two identical daughter molecules of DNA Nucleotides Both parental strands serve as templates Parental molecule of DNA A template mode for DNA replication Untwisting and replication of DNA semiconservativel Figure 10.4A A template model for DNA replication. This figure emphasizes the accuracy of DNA replication, due to the specific base-pairing interactions. When the strand on the left is a template, the complementary strand is identical to the one on the right and vice versa.

10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits A gene is a sequence of DNA that directs the synthesis of a specific protein DNA is transcribed into RNA RNA is translated into protein The presence and action of proteins determine the phenotype of an organism The role of proteins in expression of a genotype can be connected to the experiments that established the foundations of genetics. The round-wrinkled phenotypes of Mendel’s pea plants were due to differences in the production of a Starch Branching Enzyme (SBEI). The round-seeded plants had a functional version of the SBEI enzyme, allowing the formation of amylopectin, a highly branched form of starch, from sucrose. The wrinkled-seeded plants stored excess sucrose due to their lack of a functional SBEI enzyme and accumulated excess water as a result. When both types of seeds completed a natural dehydration process in seed maturation, the round seeds retained their shape, while the wrinkled seeds shriveled from water loss. Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Consider placing the basic content from Figure 10.6 on the board, noting the sequence, products, and locations of transcription and translation in eukaryotic cells. This reminder can create a quick concept check for students as they learn additional detail. Teaching Tips 1. It has been said that everything about an organism is an interaction between the genome and the environment. You might wish to challenge your students to explain the validity of this statement. 2. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. Copyright © 2009 Pearson Education, Inc.

Flow of genetic information in a eukaryotic cell
Translation Protein Transcription RNA Cytoplasm Nucleus Genotype DNA Phenotype Flow of genetic information in a eukaryotic cell Figure 10.6A Flow of genetic information in a eukaryotic cell. Transcription is the production of RNA using DNA as a template. In eukaryotic cells, transcription occurs in the nucleus, and the resulting RNA (mRNA) enters the cytoplasm. Translation is the production of protein, using the sequence of nucleotides in RNA. Translation occurs in the cytoplasm for both prokaryotic and eukaryotic cells.

Each “word” is a codon, consisting of three nucleotides
10.7 Genetic information written in codons is translated into amino acid sequences The sequence of nucleotides in DNA provides a code for constructing a protein Protein construction requires a conversion of a nucleotide sequence to an amino acid sequence Transcription rewrites the DNA code into RNA, using the same nucleotide “language” Each “word” is a codon, consisting of three nucleotides Translation involves switching from the nucleotide “language” to amino acid “language” Each amino acid is specified by a codon 64 codons are possible Some amino acids have more than one possible codon Comparing the linguistic meaning of transcription and translation is a useful analogy for the biochemical processes. Transcription involves staying in the nucleic acid language, while translation involves converting nucleotide codes into the amino acid language of proteins. I suggest that a student whose native language is not English may transcribe the words of an instructor during the lecture presentation, and then translate those words into his or her native language for better understanding. I also relate a story about purchasing a recipe book in French and not being able to make any of the dishes without translating the information into English! Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. The transcription of DNA into RNA is like a reporter who transcribes a political speech. In both situations, the language remains the same, although in the case of the reporter, it changes its form from spoken to written language. 2. The sequential information in DNA and RNA is analogous to the sequential information in the letters of a sentence. This analogy is also helpful when explaining the impact of insertion or deletion mutations that cause a shift in the reading frame (see Module 10.16). Copyright © 2009 Pearson Education, Inc.

Transcription & translations of codons
DNA molecule جزيء دنا Gene 1 جين 1 Transcription & translations of codons نسخ وترجمة وحدات الشفرة الوراثية Gene 2 جين 2 Gene 3 جين 3 DNA strand خيط الدنا Figure 10.7 Transcription and translation of codons. Transcription النسخ RNA الرنا Codon وحدة الشفرة Translation الترجمة Polypeptide متعدد البيبتيدات Amino acid حمض أميني

10.8 The genetic code is the Rosetta stone of life
Characteristics of the genetic code Triplet: Three nucleotides specify one amino acid 61 codons correspond to amino acids AUG codes for methionine and signals the start of transcription 3 “stop” codons signal the end of translation UAA UGA UAG Exceptions to the universality of the genetic code are found for both mitochondrial and nuclear genes. In mitochondria from animals and microorganisms such as yeast, UGA codes for tryptophan rather than stop. In vertebrate mitochondria, AGA and AGG are stop codons instead of specifying arginine. In yeast mitochondria, all codons beginning with CU code for threonine instead of leucine, while the codons UUA and UUG still specify leucine. For the nuclear genes of the ciliated protozoan Tetrahymena thermophila, UAA and UAG code for glutamine rather than stop. Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. The authors note the parallel between the discovery in 1799 of the Rosetta stone, which provided the key that enabled scholars to crack the previously indecipherable hieroglyphic code, and the cracking of the genetic code in Consider challenging your students to explain what part of the genetic code is similar to the Rosetta stone. This could be a short in-class activity for small groups. 2. The authors note the universal use of the genetic code in all forms of life. The evolutionary significance of this fundamental, universal language is a reminder of the shared ancestry of all life. The universal genetic code is part of the overwhelming evidence for evolution. Copyright © 2009 Pearson Education, Inc.

10.8 The genetic code is the Rosetta stone of life
Redundant: More than one codon for some amino acids Unambiguous: Any codon for one amino acid does not code for any other amino acid Nearly universal Exceptions to the universality of the genetic code are found for both mitochondrial and nuclear genes. In mitochondria from animals and microorganisms such as yeast, UGA codes for tryptophan rather than stop. In vertebrate mitochondria, AGA and AGG are stop codons instead of specifying arginine. In yeast mitochondria, all codons beginning with CU code for threonine instead of leucine, while the codons UUA and UUG still specify leucine. For the nuclear genes of the ciliated protozoan Tetrahymena thermophila, UAA and UAG code for glutamine rather than stop. Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. The authors note the parallel between the discovery in 1799 of the Rosetta stone, which provided the key that enabled scholars to crack the previously indecipherable hieroglyphic code, and the cracking of the genetic code in Consider challenging your students to explain what part of the genetic code is similar to the Rosetta stone. This could be a short in-class activity for small groups. 2. The authors note the universal use of the genetic code in all forms of life. The evolutionary significance of this fundamental, universal language is a reminder of the shared ancestry of all life. The universal genetic code is part of the overwhelming evidence for evolution. Copyright © 2009 Pearson Education, Inc.

Dictionary of the genetic code (RNA codons)
First base Third base Second base Dictionary of the genetic code (RNA codons) Figure 10.8A Dictionary of the genetic code (RNA codons). This listing of the codon “dictionary” can be used to illustrate the triplet and redundant nature of the code. While methionine and tryptophan have only one codon each, leucine, serine, and arginine each have six codons. It can also be pointed out that codons for the same amino acid often differ in the third nucleotide, a phenomenon described as “wobble.” The base pairing of the first two nucleotides of the codon with corresponding positions in the anticodon is stringent, but pairing of the third is weaker and more flexible. The wobble hypothesis proposed by Francis Crick allows for some nonstandard pairings that account for some of the redundancy of the genetic code. For example, if the third position of the codon is a U or C, it can pair with a G on the anticodon. This would mean that one tRNA, rather than two, could be used to translate UUU and UUC, for example. Estimates of 30–50 tRNAs necessary to pair with 61 codons are borne out by studies that identify 45 different tRNAs in some cell types.

Strand to be transcribed Deciphering the genetic information in DNA
RNA Polypeptide Translation Met Lys Phe Start codon Transcription Stop codon Strand to be transcribed Deciphering the genetic information in DNA Figure 10.8B Deciphering the genetic information in DNA.

10.16 Mutations can change the meaning of genes
A mutation is a change in the nucleotide sequence of DNA Base substitutions: replacement of one nucleotide with another Effect depends on whether there is an amino acid change that alters the function of the protein Deletions or insertions: Alter the reading frame of the mRNA, so that nucleotides are grouped into different codons Lead to significant changes in amino acid sequence downstream of mutation Cause a nonfunctional polypeptide to be produced Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolution mechanisms. In this sense, mutations may be considered a part of a positive creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Copyright © 2009 Pearson Education, Inc.

10.16 Mutations can change the meaning of genes
Mutations can be Spontaneous: due to errors in DNA replication or recombination Induced by mutagens High-energy radiation Chemicals Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolution mechanisms. In this sense, mutations may be considered a part of a positive creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Copyright © 2009 Pearson Education, Inc.

Sickle-cell hemoglobin The molecular basis of Sickle-cell disease
Normal hemoglobin DNA Mutant hemoglobin DNA * mRNA mRNA Normal hemoglobin Sickle-cell hemoglobin Figure 10.16A The molecular basis of sickle-cell disease. This figure shows the base pair change that leads to the formation of sickle cell hemoglobin. This results in an amino acid change in the protein, from glutamic acid to valine. This substitution of a hydrophobic amino acid for a hydrophilic one causes a significant difference in the activity of the -hemoglobin chain. Normal hemoglobin molecules exist as individual units whether they are bound to oxygen or not. Sickle cell hemoglobin molecules are also single entities when oxygen is bound, but they form large polymers that distort the shape of the cell when oxygen is released to the tissues. The cells may have an irregular appearance or assume the crescent or sickle shape for which the disease is named. These misshapen cells tend to clog blood vessels, leading to pain, infection, and damage to organs. Cells with sickle cell hemoglobin have a shorter lifetime than normal cells (10–20 days as opposed to 3 months) so anemia sets in because the bone marrow is unable to produce new cells as rapidly as they are removed from the population. This example demonstrates that a seemingly small change, a difference of one base pair leading to a change in a single amino acid (out of 147), can have severe effects. Glu * Val The molecular basis of Sickle-cell disease

Types of mutations and their effects
Normal gene Protein Base substitution Base deletion Missing mRNA Met Lys Phe Ser Ala Gly Leu His Types of mutations and their effects Figure 10.16B Types of mutations and their effects. This figure contrasts the multiple amino acid changes caused by a deletion with the single amino acid change caused by a substitution.

الأساس الخلوي للتكاثر والوراثة المصطلــــــــــــــح
Chapt. 8: The Cellular Basis of Reproduction and Inheritance الأساس الخلوي للتكاثر والوراثة تعريف المصطلـــــح المصطلــــــــــــــح التكاثر اللا جنسي Asexual Reproduction التكاثر الجنسي Sexual Reproduction الانشقاق الثنائي ”الانقسام إلى نصفين“ Binary Fission الخلايا أولية النواة Prokaryotic Cell ينتج خليتين متماثلتين من خلية واحدة Two Identical Cells Arise From One Cell الكروموزوم Chromosome يتضاعف Duplicates نسخ Copy تستطيل الخلية Cell Elongates غشاء البلازما Plasma Membrane حقيقية النواة Eukaryotic دورة الخلية Cell Cycle الانقسام الفتيلي(اللا انتصافي) Mitosis مادة الكروماتين Chromatin الكروماتين = دنا + بروتينات Chromatin = DNA + Proteins يتكثف الكروماتين بدرجة علية = الكروموزومات Compact Chromatin = Chromosomes

المصطلــــــــــــــح
تعريف المصطلـــــح المصطلــــــــــــــح الكروموزومات المضاعفه= كروماتيدياتين شقيقين كل منهما بحوي جزئ واحد من الدنا متماثل لشقيقة Duplicated Chromosomes= Two Sister Chromatids المنطقة المركزية الضيقة في الكروموروم Centromere الطور البيني في دورة الخلية Interphase Of The Cell Cycle مرحلة نمو1 في دورة الخليه Of The Cell Cycle G1 مرحلة تخليق الدنا- مضاعفة الكروموزومات S Ps Phase Of The Cell Cycle=Synthesis Of DNA (Duplication Of Chromosomes) مرحلة نمو2 في دورة الخليه G1Of The Cell Cycle الانقسام الفتيلي (اللاانتصافي) Mitotic Division الانقسام الفتيلي= انقسام النواة Mitosis=Division Of The Nucleus انقسام السيتوبلازم= الانقسام السيتوبلازمي Cytokinesis= Division Of Cytoplasm جسم مركزي Centrosomes خيوط مغزلبه Spindle Fibers غلاف نووي Nuclear Envelope النوية Nucleolus أنيبيات دقيقة مغزلية Spindle Microtubule مركز الحركة في المنطقه المركزيه للكروموزوم Kinetochore

تعريف المصطلـــــح المصطلــــــــــــــح الطور الاستوائي Metaphase الطور الانفصالي Anaphase الطور النهائي Telophase التخصر Cleavage Furrow الصفيحة الخلوية Cell Plate الخيوط الدقيقة Microfilaments نمو Growth بصل Onion جذور Roots الانقسام الاختزالي ( الأنتصافي) Meiosis العبور الوراثي Crossing Over أزواج الكروموزومات المتماثلة Chromosomes Homologous Pairs الموضع الذي يحتله الجين على الكروموزوم Gene Location On Chromosome= Locus كروموزومات الأم Maternal Chromosomes كروموزومات الأب Paternal Chromosomes جميعها ما عد ا الكروموزومات الجسديه X , Y Autosomes الجاميطات ) الامشاج ) Gametes

المصطلــــــــــــــح المصطلــــــــــــــح
تعريف المصطلـــــح المصطلــــــــــــــح احادي الصيغه الصبغيه 23 في الأنسا ن 1n (Haploid) ثنائي الصيغه الصبغيه في ألأنسان 2n )Diploid) الحيوان المنوي Sperm البيضة Egg اخصاب Fertilization اللاقحة (البيضه المُخصبة ) Zygote تلتف Coil مضغوط Compact الاقتران Synapsis أربع كروماتيدات = رباعية Tetrad Chapt.9: Patterns of Inheritance أنماط الوراثة تعريف المصطلـــــح المصطلــــــــــــــح نظرية شمولية التكوين Pangenesis الخلط Blending المادة الوراثية Hereditary Material التهجين Breeding العوامل الوراثية = الجينات Heritable Factors = Genes

تعريف المصطلـــــح المصطلــــــــــــــح الاخصاب الذاتي Self-Fertilization الاخصاب الخلطي Cross-Fertilization الذرية = النسل Offspring تهجين أحادى Monohybrid Cross الجيل الأبوي Parental Generation جيل الذرية 1الأول F1 Generation جيل الذرية الثاني F2 Generation هيئة = صفه Trait نسل اصيل غير هحين True-Breeding(BB Or Bb But Not Bb) النمط الظاهري Phenotype النسبه Ratio النمط الجينيي Genotype يوجيد نسختين من كل جين واحده من الأب والأخرى من الأم كل نسخه نسمى الييل ويمكن ان يكونوا متشابهين او مختلفين Allele= One Of The Two Copies Of A Gene سائد Dominant متنحي Recessive متمائل الألائل AA Or Aa Homozygous متغاير الألائل Aa Heterozygous

المصطلــــــــــــــح البيولوجيا الجزيئية للجين المصطلــــــــــــــح
تعريف المصطلـــــح المصطلــــــــــــــح شجرة النسب A Pedigree يستنبط Deduce رمادي سيادة غير التامة Bb Incomplete Dominance رمادي نمط مظهري وسطي Bb Intermediate Phenotype سياده مشتركه ( الزمره الدمويه AB ) Blood Group AB)) Co-Dominance الاضطرابات المتنحية ( لا بد من ان يكون كلا الأليلين لا يعملان( Recessive Disorders (Both Alleles Have To Be Defective) الاضطرابات السائدة ( يكفي خلل اليل واحد ليسبب المرض ) Dominant Disorders التعبير Expression Chapt.10 :Molecular Biology of the Gene البيولوجيا الجزيئية للجين تعريف المصطلـــــح المصطلــــــــــــــح موحود Monomer مكئور Polymer نيوكليوتيدة Nucleotide متعدد نيوكليوتيدات Polynucleotide

تعريف المصطلـــــح المصطلــــــــــــــح دنا) حمض نووي ريبوزي لااكسجيني) DNA(Deoxy Ribonucleic Acid) = Polynucleotide حلزون مزدوج الخيوط Double-Stranded Helix سلسله Chain تزاوج القواعد النيتروجينية Base Pairing التعبير الجيني Gene Expression الطي Folding, الالتفاف Coiling تعبئة Packing الأجسام النووية Nucleosomes الدنا الرابط الذي يصل ما بين الأجسام النووية Linker DNA تضاعف الدنا DNA Replication نموذج شبة تحفظي Semiconservative Model خيط مُكمل Complementary Strand قالب Template تسلسل Sequence استنساخ Transcription ترجمه Translation

البيولوجيا الجزيئية للجين المصطلــــــــــــــح
Chapt.10 :Molecular Biology of the Gene البيولوجيا الجزيئية للجين تعريف المصطلـــــح المصطلــــــــــــــح الرنا RNA( Ribonucleic Acid) شفرة Codon حامض أميني Amino Acid إشارة Signal الترادف Redundancy عدم الغموض Unambiguous فراغات أو أو فواصل او علامات وقف Spacers Or Punctuation ملتصقة Adjacent طفرة Mutation استبدال Substitutions الحذف Deletions الإضافة Insertion تلقائي Spontaneous مستحدث Induced المُطفرات Mutagens

The Cellular Basis of Reproduction and Inheritance

Similar presentations

Presentation on theme: "The Cellular Basis of Reproduction and Inheritance"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

The Cellular Basis of Reproduction and Inheritance

Similar presentations

Presentation on theme: "The Cellular Basis of Reproduction and Inheritance"— Presentation transcript:

Similar presentations

About project

Feedback