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M EIOSIS Chapter 11. R EVIEW Cell has issues when it grows larger in size Not enough DNA Nutrients and wastes cannot pass the cell membrane Cell solves.

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Presentation on theme: "M EIOSIS Chapter 11. R EVIEW Cell has issues when it grows larger in size Not enough DNA Nutrients and wastes cannot pass the cell membrane Cell solves."— Presentation transcript:

1 M EIOSIS Chapter 11

2 R EVIEW Cell has issues when it grows larger in size Not enough DNA Nutrients and wastes cannot pass the cell membrane Cell solves these problems through the process of cell division Mitosis – the portion of cell division where the nucleus divides

3 M ITOSIS Almost every cell of the body uses mitosis to divide the nucleus Somatic cells – cells that are not sex cells/gametes Exs) liver cell, bone cell, brain cell etc. AS LONG AS IT IS NOT SPERM OR EGGS IT USES MITOSIS Cell grows (G1), synthesizes DNA (S), makes molecules and organelles (G2) and then is ready for cell division (mitosis and cytokinesis)

4 S TAGES OF M ITOSIS 1. Prophase – chromatin condenses into chromosomes and nuclear envelope breaks down, centrioles move and spindle fibers form 2. Metaphase – chromosomes line up in middle of cell and spindle fibers attach to centromere PROPHASE

5 S TAGES OF M ITOSIS 3. Anaphase – spindle fibers pull at centromere and separate sister chromatids pulling them to opposite ends of the cell 4. Telophase – chromosomes break down into chromatin and nuclear envelope reforms

6 T HE END OF M ITOSIS After telophase, the cells cytoplasm splits by the process of cytokinesis As a result we are left with… 2 IDENTICAL DAUGHTER CELLS

7 T HE N EW S TUFF … There are many studies into the process that makes each one of us different Gregor Mendel – a monk born in 1822 who did many studies in the field of genetics Genetics – the study of heredity Why is it that we have traits (eye color, hair color, etc.) similar to our parents, yet we are not all alike?

8 G ENETICS Mendel recognized that the offspring of “parents” were similar and began to investigate why this happens He came to the conclusion that the parent organisms must pass on traits in their genetic material These traits are located on their genes (DNA)

9 M ENDEL ’ S P REDICTIONS Mendel was correct about the passing of traits and the idea of genes He wasn’t sure how these events happened but knew 1. An organism must inherit a single copy of every gene from both its “parents” 2. When and organism produces its own cells to pass to offspring, there are 2 sets that must separate from each other so that each cell contains just 1 set of genes

10 STOP! W HAT DOES THIS MEAN ?!?! Gametes – the sex cells of an organism Sperm and eggs Mitosis deals with non-gametes (somatic cells) Remember, in mitosis we result in genetically identical cells WE DO NOT WANT GENETICALLY IDENTICAL OFFSPRING!!!

11 T RANSLATION OF M ENDEL ’ S I DEA #2 When and organism produces its own cells to pass to offspring, there are 2 sets that must separate from each other so that each cell contains just 1 set of genes Every cell of the human body contains a specific number of chromosomes (46) In order for offspring to maintain that number of 46 and not end up with duplicate (92), the parent gamete (sex cell) must half their number of chromosomes End result > 23 (mom) + 23 (dad) = 46 offspring chromosomes

12 T RANSLATION OF M ENDEL ’ S I DEA #1 An organism must inherit a single copy of every gene from both its “parents” Remember, each of the 46 chromosomes needs to halved by the parents (to make 23) Parents will only contribute each of those 23 genes one time to their offspring (parents do not want to give multiple copies of the same gene) So, again = 46 chromosomes total

13 C HROMOSOMES AND GAMETES Remember… Chromosomes – the structures in the cell that carry the genetic material (genes) from the parent cell to the daughter cell Gametes – sex cells or germ cells (sperm and egg)

14 C HROMOSOMES There are many chromosomes in the body that carry information for many different “things” Examples – eye color, hair color, height, 2 nd toe length, etc… (everything that makes you, you!) When 2 cells come together from 2 parents, the matching chromosomes must come in contact These matching chromosomes are called homologus Homologous Chromosomes – same chromosome types between mother and father cells

15 C HROMOSOME N UMBERS Haploid – a cell that contains a single set of chromosomes Remember “hap” sounds like half Is usually represented as N Diploid – a cell that contains both sets of homologous chromosomes Remember “di” means 2 (kinda like “bi” – bicycle) Is usually represented as 2N Since the somatic cells of the body are diploid we need the sex cells to be haploid so offspring do not have more chromosomes than necessary

16 W HAT DO D IPLOID /H APLOID N UMBERS M EAN ? Diploid Barbie 2N = 46 chromosomes Diploid Ken 2N = 46 chromosomes Equals Diploid Baby 2N = 46 chromosomes Haploid Barbie Cell N = 23 chromosomes Haploid Ken Cell N = 23 chromosomes + Sperm cell Egg cell

17 H OW ARE H APLOID G AMETES P RODUCED ? Meiosis a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell Involves 2 distinct divisions 1. Meiosis 1 2. Meiosis 2 Starts with 1 diploid cell and results in 4 haploid daughter cells that are GENETICALLY DIFFERENT from the parent cell

18 M EIOSIS 1 Prior to meiosis 1, each chromosome is replicated Same as S phase of interphase prior to mitosis Meiosis 1 starts with the cell beginning to divide very similarly to mitosis Unlike mitosis, meiosis 1 has homologous pairing in each step Homologous Pairing – the same chromosome types from mom and dad come together (eye color, hair color, etc.)

19 P ROPHASE 1 Homologous chromosomes pair and form a tetrad Since 1 chromosome is made of 2 chromatids, there are 4 chromatids in a tetrad While in their tetrad, homologous chromosomes are able to trade/swap information in a process called crossing over this process results in the exchange of traits (alleles) between the same chromosomes therefore creating new trait combinations One reason why you are different from your parents!

20 R EMAINDER OF M EIOSIS 1 Meiosis utilizes the remainder of the cycles as mitosis did separating homologous chromosomes instead of sister chromatids Metaphase 1 – spindle fibers attach to homologous chromosomes Anaphase 1 – spindle fibers separate homologous chromosomes

21 R EMAINDER OF M EIOSIS 1 Telophase 1/Cytokinesis – the nuclear envelope reforms around chromosomes and the cytoplasm splits As a result of Meiosis 1, 2 daughter cells are produced tat have half the number of genetically different chromosomes

22 M EIOSIS 2 After Meiosis 1, the 2 cells produced proceed to meiosis 2 (there is no chromosome replication) Each of the daughter cells move through Meiosis 2 much in the same way Mitosis occurs Prophase 2 – the centriole move to opposite ends of the cell, the nuclear envelope breaks down Metaphase 2 – chromosomes line up in the middle of the cell and spindle fibers attach to the centromere

23 M EIOSIS 2 Anaphase 2 – the spindle fibers pull on the centromere and split the sister chromatids Telophase 2 & Cytokinesis – the nuclear envelope forms and the cell cytoplasm splits 4 genetically DIFFERENT cells result

24 G AMETE F ORMATION The male gamete that is produced is called a sperm (spermatocyte) There are 4 sperm cells that are produced as a result of meiosis The female gamete that is produced is called an egg (oocyte) There is 1 egg cell produced as a result of meiosis The 3 other cells produced are called polar bodies Polar Bodies are not used in reproduction and are considered to be the trash bags of the egg, but can be useful in genetic testing

25 C OMPARING M ITOSIS AND M EIOSIS Sloppy Copy Mitosis/Meiosis Picture Fold paper down middle Draw Mitosis on left side starting with interphase and ending with cytokinesis beginning with 4 chromosomes (X’s) Draw Meiosis on right side starting with interphase and ending with cytokinesis 2 beginning with 4 chromosomes (X’s) Mitosis/Meiosis Compare/Contrast Graphic Organizer 3 ways they are similar 3 ways they are different

26 T HE W ORK OF G REGOR M ENDEL Every living thing has a set of characteristics inherited from its parent(s) Genetics – study of heredity The father of genetics was Gregor Mendel Was an Austrian monk that studies the passing of traits in pea plants

27 G REGOR M ENDEL ’ S P EA P LANTS He was put in charge of the gardens at the monastery He knew how the process of fertilization occurred When the male and female cells join during sexual reproduction In plants fertilization happens because of pollination

28 C REATING P LANTS Pea plants are able to self-pollinate The sperm in the pollen can fertilize the egg cell of the same plant As a result, a plant can be created from only 1 “parent” and therefore have the same characteristics of that 1 parent Since plants were self-pollinating, they would also be considered true-breeding They would produce offspring identical to themselves Ex) tall plants would make more tall plants Ex) green seeded plants would make more green seeded plants

29 M ENDEL ’ S G ETS S TARTED Even though true-breeding plants are good, Mendel was interested in what would happen if different traits were “crossed” Mendel manipulated flowers so they could not self-pollinate and then began to cross breed plants with different characteristics Ex) cross a tall plant with a short plant Ex) cross a yellow seed plant with a green seed plant

30 G ENES AND D OMINANCE Mendel studied contrasting pea plant traits Trait – a specific characteristic (such as color or height) that varies from one individual to another Mendel looked at the offspring that he created by crossing parents with different traits These offspring were called hybrids P – symbol for the parental generation F1 – symbol for the 1 st generation

31 W HAT D ID THE 1 ST G ENERATION L OOK L IKE ? To Mendel’s surprise, the offspring were not a combination of the 2 different traits One of the traits did not even appear

32 M ENDEL ’ S C ONCLUSIONS 1. Biological inheritance is determined by factors that are passed from one generation to the next We know that this is because of genes – chemical factors that determine traits The different forms of a gene is an allele Ex) alleles of height – tall & short alleles of color – yellow & green 2. Some alleles are dominant and others are recessive (principal of dominance) Dominant traits will be exhibited whenever present Recessive traits will only be exhibited when it’s the only trait present

33 S EGREGATION Mendel wanted to know if the recessive trait had completely disappeared in the F1 generation He allowed the F1 generation plants to cross by self-pollination, creating a F2 generation

34 F1 C ROSS R ESULTS Mendel discovered the recessive traits reappeared Mendel concludes that the dominant allele had only masked the recessive allele and that recessive alleles never disappeared The alleles must separate or segregate from each other Gametes pick up one allele or another during the segregation process

35 H OW D ID S EGREGATION W ORK ? Mendel concludes: When each of the F1 plant flowers produces gametes, the two alleles segregate from each other so that each gamete carries only a single copy of each gene Therefore, each F1 plant produces 2 types of gametes – those with the allele for tallness and those with the allele for shortness

36 M ENDEL ’ S R ESULTS Mendel repeated his experiments many times to see what would happen He realized that for each cross, he got the same basic results Ex) whenever he crossed Tt for height, ¾ of offspring were tall and ¼ of offspring were short Mendel realized that he could apply the principals of probability to explain the results of genetic crosses

37 G ENETICS AND P ROBABILITY Probability – the likelihood that a particular event will occur Example – Coin Flip The chances that a coin will come up heads is 50% (1/2 or 1:2) The chances that a coin will come up tails is 50% (1/2 or 1:2) If you flipped a coin and it came up heads, what are the chances that it will come up heads the next time? The next time? Each event is independent of each other, so each time is a 50% chance

38 C OIN T OSS A CTIVITY Hypothesis: If I toss a coin 2 times, I would expect to get _______ Heads and ________ Tails. Toss your coin 2 times and record results Toss 1 ____ H _____ T Toss 2 ____ H _____ T Toss your coin 8 more times and record results Toss 3 Toss 4 Toss 5 Toss 6 Toss 7 Toss 8 Toss 9 Toss 10

39 A CTUAL C OIN T OSS R ESULTS For first 2 tosses: Number Heads ______ Number Tails ______ Total Results Number Heads ______ Number Tails ______ Did the actual results for the entire class come closer to your hypothesis of 50/50 chance for heads and tails?

40 H OW IS C OIN F LIPPING R ELEVANT TO G ENETICS ? When we are dealing with probabilities of an event, past outcomes DO NOT affect future ones Each event is completely separate and therefore has just as equal chances for an outcome as the one before The segregation of alleles is completely random, just like a coin toss You randomly get what you get, every single time

41 P UNNETT S QUARES Punnett Square – is a diagram that shows the gene combinations that can result from a genetic cross Dominant traits are expressed by capital letters (T) Recessive traits are expressed by lower case letters (t) Homozygous – organisms that have identical alleles for a particular trait (TT or tt) Are true breeding (pure-bred) organisms for a trait Heterozygous – organisms that have different alleles for a particular trait (Tt) Are hybrid organisms for a particular trait

42 P UNNETT S QUARE R ESULTS The outcomes of a punnett square can be described by both their “letters” and their “appearances” Phenotype – the physical characteristics of an organism (the appearance) Ex) tall, short, yellow, green Genotype – the genetic makeup of an organism (the letters) Ex) TT, Tt, tt Organisms can have the same phenotype even though they have different genotypes TT – tall & Tt – tall

43 P ROBABILITY AND S EGREGATION Was Mendel’s model for segregation correct when looking at alleles for height? YES! (branching tree example) Are we able to determine the same results by looking at probabilities for height? YES (punnett square example) The results are the same no matter how you look at it

44 P ROBABILITIES P REDICT A VERAGES Probabilities can predict the average outcome of a large number of events ( remb. the coin tossing ) They cannot predict the precise outcome of an individual event The predictions are based on chances for each individual event When dealing with genetics, the larger the number of offspring, the closer your results will be to the predicted number

45 I NDEPENDENT A SSORTMENT Mendel said that alleles segregate during the formation of gametes When Mendel was doing his experiments he wanted to know if alleles segregated on their own (independently) or if one allele can affect another allele Mendel goes back to the pea plant to find the answer

46 2 F ACTOR C ROSSES – F1 Mendel performed his pea plant experiments now looking at 2 different traits at once Mendel crossed purebred plants round yellow (RRYY) and wrinkled green (rryy) [P] and looked at their offspring [F1] All offspring were heterozygous round yellow (RrYy) We are not able to see if the alleles segregate independently with these results…

47 2 F ACTOR C ROSS – F2 Mendel crossed 2 of the F1 offspring to create a F2 generation Mendel wanted to know if dominant/recessive alleles stay together (RY/ry) Mendel looked at the F2 results and saw… 9/16 were round yellow 3/16 were round green 3/16 were wrinkled yellow 1/16 was wrinkled green Remember our P generation genotypes… RRYY – round yellow rryy – wrinkled green

48 F2 R ESULTS Mendel saw in the F2 generation the presence of offspring that did not exist in any parent Round green and wrinkled yellow This fact means that alleles are capable of segregate independently Independent Assortment – genes for different traits are able to separate on their own and do not influence each others inheritance the alleles for seed shape and color did not influence each other since they were capable of separation

49 P RINCIPAL OF I NDEPENDENT A SSORTMENT This states… Genes for different traits can segregate independently during the formation of gametes Along with crossing over, independent assortment is the other process that accounts for genetic variation

50 S UMMARY OF M ENDEL ’ S P RINCIPALS The inheritance of biological characteristics is determined by individual units known as genes. Genes are passes from parents to offspring In cases in which 2 or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. In most sexually reproducing organisms, each adult has 2 copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed The alleles for different genes usually segregate independently of one another.

51 B EYOND D OMINANT AND R ECESSIVE There are some exceptions to some of Mendel’s principals Since many genes have more than 2 alleles and many traits are controlled by more than 1 gene, genetics can be very complicated Genetics deals with more than just dominance and recessiveness

52 P ATTERNS OF I NHERITANCE ( HOW GENES ARE INHERITED ) Incomplete Dominance – when one allele is not completely dominant and another completely recessive The offspring will be a mixture of 2 phenotypes Ex) some flowers with red and white parents will result with a pink phenotype Codominance – both alleles contribute to the phenotype of an organism The offspring will show more than 1 phenotype Ex) a white chicken and a black chicken have offspring that are black and white “speckled”

53 P ATTERNS OF I NHERITANCE ( HOW GENES ARE INHERITED ) Multiple Alleles – when genes have more than one allele possibility The individual will not have more than 2 allele, there are just more than 2 possibilities in the population Ex) coat color in rabbits Polygenic Traits – traits that are controlled by 2 or more genes Traits can be produced by the interaction of genes Ex) fly eye color, skin color, coat color in labs

54 A PPLYING M ENDEL ’ S P RINCIPALS There are many scientists that tried to test Mendel’s principals Thomas Hunt Morgan – a scientist from the early 1900’s that performed genetic tests on fruit flies Why Fruit Flies? Small organism (easy to care for and doesn’t take up much room) Reproduces quickly Inexpensive to get and keep Fruit flies will prove to be very important to the study of genetics!!

55 G ENETIC AND THE E NVIRONMENT Characteristics of organisms are not determined by genetics alone The interaction of organisms and the environment can play a role in genetics Height of plants determined by the sun Evolution of organisms based on surroundings The development of disease based on contact with different substances in environment “genes provide a plan, how plan unfolds depends on environment”

56 G ENE L INKAGE We have been able to look at how genes located on different chromosomes assort independently What happens to genes on same chromosomes Do they assort? Must they be inherited together? These questions were tested by Thomas Hunt Morgan with his fruit fly research

57 G ENE L INKAGE IN D ROSOPHILA MELANOGASTER Morgan was able to identify more than 50 genes He saw that many genes were inherited together Ex) many times reddish-orange eyes and small wings were almost always inherited together and were rarely separated Does this mean independent assortment doesn’t occur? Through much research, Morgan discovered 4 linkage groups

58 G ENE L INKAGE IN D ROSOPHILA MELANOGASTER When Morgan crossed the linkage groups, he realized… that the linkage groups assorted independently all of the genes that were involved with the linkage group were inherited together This information leads to 2 conclusions 1. Each chromosome is actually a group of linked genes 2. It is the chromosome that assorts independently, not the gene Mendel didn’t see gene linkage because the genes he was looking at were on different chromosomes

59 G ENE M APS Just because genes are found on the same chromosome, does not mean that they are linked forever Crossing-over can separated genes on same chromosomes producing new alleles Researchers of Morgan’s looked at the rate at which linked genes were separated and used their findings to produce gene maps Gene map – shows the relative locations of each gene on a chromosome Crossing-over rates were used to construct the drosophila and human genome map


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