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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece.

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Presentation on theme: "Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece."— Presentation transcript:

1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 13 Meiosis and Sexual Life Cycles

2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Hereditary Similarity and Variation Living organisms are distinguished by their ability to reproduce their own kind Heredity is the transmission of traits from one generation to the next Variation shows that offspring differ in appearance from parents and siblings Genetics is the scientific study of heredity and variation

3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

4 Concept 13.1: Offspring acquire genes from parents by inheriting chromosomes In a literal sense, children do not inherit particular physical traits from their parents It is genes that are actually inherited

5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inheritance of Genes Genes are the units of heredity Genes are segments of DNA Each gene has a specific locus on a certain chromosome One set of chromosomes is inherited from each parent Reproductive cells called gametes (sperm and eggs) unite, passing genes to the next generation

6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparison of Asexual and Sexual Reproduction In asexual reproduction, one parent produces genetically identical offspring by mitosis In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents Video: Hydra Budding Video: Hydra Budding

7 LE 13-2 Parent 0.5 mm Bud

8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 13.2: Fertilization and meiosis alternate in sexual life cycles A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism

9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sets of Chromosomes in Human Cells Each human somatic cell (any cell other than a gamete) has 46 chromosomes arranged in pairs A karyotype is an ordered display of the pairs of chromosomes from a cell The two chromosomes in each pair are called homologous chromosomes, or homologues Both chromosomes in a pair carry genes controlling the same inherited characteristics

10 LE µm Pair of homologous chromosomes Sister chromatids Centromere

11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The sex chromosomes are called X and Y Human females have a homologous pair of X chromosomes (XX) Human males have one X and one Y chromosome The 22 pairs of chromosomes that do not determine sex are called autosomes

12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Each pair of homologous chromosomes includes one chromosome from each parent The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father The number of chromosomes in a single set is represented by n A cell with two sets is called diploid (2n) For humans, the diploid number is 46 (2n = 46)

13 LE 13-4 Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of chromosomes (n = 3) Two sister chromatids of one replicated chromosomes Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set) Centromere

14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gametes are haploid cells, containing only one set of chromosomes For humans, the haploid number is 23 (n = 23) Each set of 23 consists of 22 autosomes and a single sex chromosome In an unfertilized egg (ovum), the sex chromosome is X In a sperm cell, the sex chromosome may be either X or Y

15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Behavior of Chromosome Sets in the Human Life Cycle At sexual maturity, the ovaries and testes produce haploid gametes Gametes are the only types of human cells produced by meiosis, rather than mitosis Meiosis results in one set of chromosomes in each gamete Fertilization, the fusing of gametes, restores the diploid condition, forming a zygote The diploid zygote develops into an adult

16 LE 13-5 Key Haploid (n) Diploid (2n) Haploid gametes (n = 23) Ovum (n) Sperm cell (n) Testis Ovary Mitosis and development Multicellular diploid adults (2n = 46) FERTILIZATIONMEIOSIS Diploid zygote (2n = 46)

17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Variety of Sexual Life Cycles The alternation of meiosis and fertilization is common to all organisms that reproduce sexually The three main types of sexual life cycles differ in the timing of meiosis and fertilization

18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In animals, meiosis produces gametes, which undergo no further cell division before fertilization Gametes are the only haploid cells in animals Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism

19 LE 13-6 Key Haploid Diploid Gametes n Diploid multicellular organism (sporophyte) Mitosis Diploid multicellular organism FERTILIZATION MEIOSIS Zygote n n 2n2n 2n2n Animals Plants and some algae Most fungi and some protists n n n n n n n n n n FERTILIZATION MEIOSIS Gametes Zygote Mitosis 2n2n 2n2n 2n2n Spores Haploid multicellular organism (gametophyte) Haploid multicellular organism

20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plants and some algae exhibit an alternation of generations This life cycle includes two multicellular generations or stages: one diploid and one haploid The diploid organism, the sporophyte, makes haploid spores by meiosis Each spore grows by mitosis into a haploid organism called a gametophyte A gametophyte makes haploid gametes by mitosis

21 LE 13-6b Key Haploid Diploid multicellular organism (sporophyte) Plants and some algae n n n n n FERTILIZATION MEIOSIS Gametes Zygote Mitosis 2n2n 2n2n Spores Haploid multicellular organism (gametophyte)

22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In most fungi and some protists, the only diploid stage is the single-celled zygote; there is no multicellular diploid stage The zygote produces haploid cells by meiosis Each haploid cell grows by mitosis into a haploid multicellular organism The haploid adult produces gametes by mitosis

23 LE 13-8b Cleavage furrow MEIOSIS II: Separates sister chromatids PROPHASE II METAPHASE IIANAPHASE II TELOPHASE I AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS Sister chromatids separate Haploid daughter cells forming Two haploid cells form; chromosomes are still double During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes

24 LE 13-9 Propase Duplicated chromosome (two sister chromatids) Chromosome replication 2n = 6 Parent cell (before chromosome replication) Chromosome replication MITOSISMEIOSIS Chiasma (site of crossing over) MEIOSIS I Prophase I Tetrad formed by synapsis of homologous chromosomes Tetrads positioned at the metaphase plate Metaphase I Chromosomes positioned at the metaphase plate Metaphase Anaphase Telophase Homologues separate during anaphase I; sister chromatids remain together Sister chromatids separate during anaphase Daughter cells of meiosis I Haploid n = 3 Anaphase I Telophase I MEIOSIS II Daughter cells of mitosis 2n2n 2n2n n Sister chromatids separate during anaphase II n nn Daughter cells of meiosis II

25 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PropertyMitosisMeiosis DNA replication During interphase DivisionsOneTwo Synapsis and crossing over Do not occurForm tetrads in prophase I Daughter cells, genetic composition Two diploid, identical to parent cell Four haploid, different from parent cell and each other Role in animal body Produces cells for growth and tissue repair Produces gametes

26 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Origins of Genetic Variation Among Offspring The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation Three mechanisms contribute to genetic variation: – Independent assortment of chromosomes – Crossing over – Random fertilization

27 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Crossing Over Crossing over produces recombinant chromosomes, which combine genes inherited from each parent Crossing over begins very early in prophase I, as homologous chromosomes pair up gene by gene In crossing over, homologous portions of two nonsister chromatids trade places Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome Animation: Genetic Variation Animation: Genetic Variation

28 LE Prophase I of meiosis Tetrad Nonsister chromatids Chiasma, site of crossing over Recombinant chromosomes Metaphase I Metaphase II Daughter cells

29 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Random Fertilization Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg) The fusion of gametes produces a zygote with any of about 64 trillion diploid combinations Crossing over adds even more variation Each zygote has a unique genetic identity

30 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary Significance of Genetic Variation Within Populations Natural selection results in accumulation of genetic variations favored by the environment Sexual reproduction contributes to the genetic variation in a population, which ultimately results from mutations

31 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

32 Concept 14.1: Mendel used the scientific approach to identify two laws of inheritance Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments

33 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mendels Experimental, Quantitative Approach Advantages of pea plants for genetic study: – There are many varieties with distinct heritable features, or characters (such as color); character variations are called traits – Mating of plants can be controlled – Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels) – Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another

34 LE 14-2 Removed stamens from purple flower Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower Carpel Stamens Parental generation (P) Pollinated carpel matured into pod Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F 1 )

35 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mendel chose to track only those characters that varied in an either-or manner He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate)

36 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization The true-breeding parents are the P generation The hybrid offspring of the P generation are called the F 1 generation When F 1 individuals self-pollinate, the F 2 generation is produced

37 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Law of Segregation When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F 1 hybrids were purple When Mendel crossed the F 1 hybrids, many of the F 2 plants had purple flowers, but some had white Mendel discovered a ratio of about three to one, purple to white flowers, in the F 2 generation

38 LE 14-3 P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers

39 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

40 The first concept is that alternative versions of genes account for variations in inherited characters For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers These alternative versions of a gene are now called alleles Each gene resides at a specific locus on a specific chromosome

41 LE 14-4 Allele for purple flowers Homologous pair of chromosomes Allele for white flowers Locus for flower-color gene

42 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The second concept is that for each character an organism inherits two alleles, one from each parent Mendel made this deduction without knowing about the role of chromosomes The two alleles at a locus on a chromosome may be identical, as in the true-breeding plants of Mendels P generation Alternatively, the two alleles at a locus may differ, as in the F 1 hybrids

43 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The third concept is that if the two alleles at a locus differ, then one (the dominant allele) determines the organisms appearance, and the other (the recessive allele) has no noticeable effect on appearance In the flower-color example, the F 1 plants had purple flowers because the allele for that trait is dominant

44 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The fourth concept, now known as the law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis

45 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mendels segregation model accounts for the 3:1 ratio he observed in the F 2 generation of his numerous crosses The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele

46 LE 14-5_2 Appearance: P Generation Genetic makeup: Gametes F 1 Generation Appearance: Genetic makeup: Gametes: F 2 Generation Purple flowers Pp P p P p F 1 sperm F 1 eggs PPPp pp P p 3: 1 Purple flowers PP White flowers pp P p

47 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Useful Genetic Vocabulary An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character Unlike homozygotes, heterozygotes are not true- breeding

48 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Because of the different effects of dominant and recessive alleles, an organisms traits do not always reveal its genetic composition Therefore, we distinguish between an organisms phenotype, or physical appearance, and its genotype, or genetic makeup

49 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Testcross How can we tell the genotype of an individual with the dominant phenotype? Such an individual must have one dominant allele, but the individual could be either homozygous dominant or heterozygous The answer is to carry out a testcross: breeding the mystery individual with a homozygous recessive individual If any offspring display the recessive phenotype, the mystery parent must be heterozygous

50 LE 14-7 Dominant phenotype, unknown genotype: PP or Pp? If PP, then all offspring purple: pp P P Pp If Pp, then 1 2 offspring purple and 1 2 offspring white: pp P P pp Pp Recessive phenotype, known genotype: pp

51 LE 14-8 P Generation F 1 Generation YYRR Gametes YR yr yyrr YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Sperm Eggs YR Yr yrYR yr Eggs YYRRYyRr yyrr yR yr Phenotypic ratio 3:1 F 2 Generation (predicted offspring) YYRR YYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr Phenotypic ratio 9:3:3:1 YRYryRyr Sperm

52 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 14.2: The laws of probability govern Mendelian inheritance Mendels laws of segregation and independent assortment reflect the rules of probability When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss

53 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Multiplication and Addition Rules Applied to Monohybrid Crosses Segregation in a heterozygous plant is like flipping a coin: Each gamete has a 1/2 chance of carrying the dominant allele and a 1/2 chance of carrying the recessive allele

54 LE 14-9 Segregation of alleles into eggs Rr Sperm Rr R r R R R r Eggs r R r r Segregation of alleles into sperm Rr

55 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Spectrum of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two parental varieties

56 LE Red C R Gametes P Generation CRCR CWCW White C W Pink C R C W CRCR Gametes CWCW F 1 Generation F 2 Generation Eggs CRCR CWCW CRCR CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW CWCW Sperm

57 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Relation Between Dominance and Phenotype A dominant allele does not subdue a recessive allele; alleles dont interact Alleles are simply variations in a genes nucleotide sequence

58 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Frequency of Dominant Alleles Dominant alleles are not necessarily more common in populations than recessive alleles For example, one baby out of 400 in the United States is born with extra fingers or toes The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage In this example, the recessive allele is far more prevalent than the dominant allele in the population

59 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multiple Alleles Most genes exist in populations in more than two allelic forms For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: I A, I B, and i. The enzyme encoded by the I A allele adds the A carbohydrate, whereas the enzyme encoded by the I B allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither

60 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

61 Pleiotropy Most genes have multiple phenotypic effects, a property called pleiotropy For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease

62 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Epistasis In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus For example, in mice and many other mammals, coat color depends on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles C for pigment color and c for no pigment color ) determines whether the pigment will be deposited in the hair

63 LE Sperm BC bCBc bc BbCcBBCcBbCCBBCC BbCC bbCCBbCc bbCc BbccBBcc BbCcBBCc BbCc bbCc Bbcc bbcc BC bC Bc bc BbCc

64 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polygenic Inheritance Quantitative characters are those that vary in the population along a continuum Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype Skin color in humans is an example of polygenic inheritance

65 LE aabbccAabbccAaBbccAaBbCcAABbCcAABBCcAABBCC AaBbCc 20 / / 64 6 / 64 1 / 64 Fraction of progeny

66 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nature and Nurture: The Environmental Impact on Phenotype Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype The norm of reaction is the phenotypic range of a genotype influenced by the environment For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity

67 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

68 Norms of reaction are generally broadest for polygenic characters Such characters are called multifactorial because genetic and environmental factors collectively influence phenotype

69 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pedigree Analysis A pedigree is a family tree that describes the interrelationships of parents and children across generations Inheritance patterns of particular traits can be traced and described using pedigrees

70 LE 14-14a Wwww Ww wwWwww Ww WWww or Ww No widows peak Third generation (two sisters) Widows peak Second generation (parents plus aunts and uncles) First generation (grandparents) Dominant trait (widows peak)

71 LE 14-14b First generation (grandparents) Ff FF or Ffff Ff ff Ff Second generation (parents plus aunts and uncles) Third generation (two sisters) Attached earlobe Free earlobe ffFF or Ff Recessive trait (attached earlobe)

72 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cystic Fibrosis Cystic fibrosis is the most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine

73 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sickle-Cell Disease Sickle-cell disease affects one out of 400 African- Americans The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells Symptoms include physical weakness, pain, organ damage, and even paralysis

74 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dominantly Inherited Disorders Some human disorders are due to dominant alleles One example is achondroplasia, a form of dwarfism that is lethal when homozygous for the dominant allele

75 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

76 Huntingtons disease is a degenerative disease of the nervous system The disease has no obvious phenotypic effects until about 35 to 40 years of age

77 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multifactorial Disorders Many diseases, such as heart disease and cancer, have both genetic and environment components Little is understood about the genetic contribution to most multifactorial diseases

78 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fetal Testing In amniocentesis, the liquid that bathes the fetus is removed and tested In chorionic villus sampling (CVS), a sample of the placenta is removed and tested Other techniques, ultrasound and fetoscopy, allow fetal health to be assessed visually in utero Video: Ultrasound of Human Fetus I Video: Ultrasound of Human Fetus I

79 LE 14-17a Amniocentesis Amniotic fluid withdrawn Fetus A sample of amniotic fluid can be taken starting at the 14th to 16th week of pregnancy. Centrifugation PlacentaUterusCervix Fluid Fetal cells Biochemical tests can be performed immediately on the amniotic fluid or later on the cultured cells. Biochemical tests Several weeks Karyotyping Fetal cells must be cultured for several weeks to obtain sufficient numbers for karyotyping.

80 LE 14-17b Chorionic villus sampling (CVS) PlacentaChorionic villi Fetus Suction tube inserted through cervix Fetal cells Biochemical tests Karyotyping and biochemical tests can be performed on the fetal cells immediately, providing results within a day or so. Several hours A sample of chorionic villus tissue can be taken as early as the 8th to 10th week of pregnancy. Karyotyping

81 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Newborn Screening Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States


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