chapter10

Meiosis and Sexual Reproduction : 

Meiosis and Sexual Reproduction Chapter 10

Impacts, Issues:Why Sex? : 

Impacts, Issues:Why Sex? An adaptive trait tends to spread more quickly through a sexually reproducing population than through an asexually reproducing one

Overview: Variations on a Theme : 

Overview: Variations on a Theme Living organisms are distinguished by their ability to reproduce their own kind Genetics is the scientific study of heredity and variation Heredity is the transmission of traits from one generation to the next Variation is demonstrated by the differences in appearance that offspring show from parents and siblings Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Concept 13.1: Offspring acquire genes from parents by inheriting chromosomes : 

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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Slide 5: 

Fig. 10-1b, p. 154

Inheritance of Genes : 

Inheritance of Genes Genes are the units of heredity, and are made up of segments of DNA Genes are passed to the next generation through reproductive cells called gametes (sperm and eggs) Each gene has a specific location called a locus on a certain chromosome Most DNA is packaged into chromosomes One set of chromosomes is inherited from each parent Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

10.1 Introducing Alleles : 

10.1 Introducing Alleles Asexual reproduction produces genetically identical copies of a parent (clones) Sexual reproduction introduces variation in the combinations of traits among offspring

Comparison of Asexual and Sexual Reproduction : 

Comparison of Asexual and Sexual Reproduction In asexual reproduction, one parent produces genetically identical offspring by mitosis A clone is a group of genetically identical individuals from the same parent In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents Video: Hydra Budding Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Genes and Alleles : 

Genes and Alleles Genes are regions in an organism’s DNA that encode information about heritable traits In sexual reproduction, pairs of genes are inherited on pairs of chromosomes, one maternal and one paternal Alleles are different forms of the same gene Offspring of sexual reproducers inherit new combinations of alleles, the basis of traits

Sets of Chromosomes in Human Cells : 

Sets of Chromosomes in Human Cells Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes 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 homologs Chromosomes in a homologous pair are the same length and carry genes controlling the same inherited characters Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Slide 11: 

Fig. 13-3b TECHNIQUE Pair of homologous replicated chromosomes Centromere Sister chromatids Metaphase chromosome 5 µm

Chromosome Pair: Maternal and Paternal : 

Chromosome Pair: Maternal and Paternal

Slide 13: 

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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

10.1 Key ConceptsSexual vs Asexual Reproduction : 

10.1 Key ConceptsSexual vs Asexual Reproduction In asexual reproduction, one parent transmits its genetic information to offspring In sexual reproduction, offspring typically inherit information from two parents who differ in their alleles Alleles are different forms of the same gene; they specify different versions of a trait

Slide 15: 

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 A diploid cell (2n) has two sets of chromosomes For humans, the diploid number is 46 (2n = 46) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

10.2 What Meiosis Does : 

10.2 What Meiosis Does Meiosis A nuclear division mechanism that precedes cytoplasmic division of immature reproductive cells in sexually-reproducing eukaryotic species

Slide 17: 

In a cell in which DNA synthesis has occurred, each chromosome is replicated Each replicated chromosome consists of two identical sister chromatids Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Slide 18: 

A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n) 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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Halving the Diploid Number : 

Halving the Diploid Number A diploid cell has two nonidentical copies of every chromosome (except XY sex chromosomes) Humans have 23 pairs of homologous chromosomes Meiosis in germ cells halves the diploid number of chromosomes (2n) to the haploid number (n), producing haploid gametes Eggs and sperm have 23 unpaired chromosomes

Slide 20: 

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 and meiosis alternate in sexual life cycles to maintain chromosome number Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Slide 21: 

Fig. 13-5 Key Haploid (n) Diploid (2n) Haploid gametes (n = 23) Egg (n) Sperm (n) MEIOSIS FERTILIZATION Ovary Testis Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

The Variety of Sexual Life Cycles : 

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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Slide 23: 

Fertilization is the union of gametes (the sperm and the egg) The fertilized egg is called a zygote and has one set of chromosomes from each parent The zygote produces somatic cells by mitosis and develops into an adult Behavior of Chromosome Sets in the Human Life Cycle Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Gamete Production : 

Gamete Production Gametes are produced in specialized reproductive structures or organs

Slide 25: 

Fig. 10-3a, p. 156 anther (where sexual spores that give rise to sperm form) ovules inside an ovary (where sexual spores that give rise to eggs form) a Flowering plant

Slide 26: 

Fig. 10-3b, p. 156 testis (where sperm originate) b Human male

Slide 27: 

Fig. 10-3c, p. 156 ovary (where eggs develop) c Human female

Restoring the Diploid Number : 

Restoring the Diploid Number Human gametes (eggs and sperm) have 23 chromosomes – one of each homologous pair The diploid number (23 pairs) is restored at fertilization, when two haploid gametes fuse and form a diploid zygote, the first cell of a new individual

Human Chromosomes: Homologous Pairs : 

Human Chromosomes: Homologous Pairs

Two Divisions, Not One : 

Two Divisions, Not One In meiosis, DNA is replicated once and divided twice (meiosis I and meiosis II), forming four haploid nuclei In meiosis I, each duplicated homologous chromosome is separated from its partner In meiosis II, sister chromatids are separated

Two Divisions, Not One : 

Two Divisions, Not One Meiosis I Meiosis II

Slide 32: 

p. 157 each chromosome in the cell pairs with its homologous partner then the partners separate

Slide 33: 

p. 157 two chromosomes (unduplicated) one chromosome (duplicated)

10.3 Visual Tour of Meiosis : 

10.3 Visual Tour of Meiosis

10.3 Visual Tour of Meiosis : 

10.3 Visual Tour of Meiosis

Slide 36: 

Fig. 10-5a, p. 158 newly forming microtubules of the spindle one pair of homologous chromosomes plasma membrane breakup of nuclear envelope centrosome with a pair of centrioles, moving to opposite sides of nucleus A Prophase I B Metaphase I C Anaphase I D Telophase I Meiosis I

Slide 37: 

Fig. 10-5a (1), p. 158

Slide 38: 

Fig. 10-5a (2), p. 158

Slide 39: 

Fig. 10-5a (3), p. 158

Slide 40: 

Fig. 10-5a (3), p. 158

Slide 41: 

Fig. 10-5a (4), p. 158

Slide 42: 

Fig. 10-5a (4), p. 158

Slide 43: 

Fig. 10-5b (1), p. 159

Slide 44: 

Fig. 10-5b (2), p. 159

Slide 45: 

Fig. 10-5b (3), p. 159

Slide 46: 

Fig. 10-5b (4), p. 159

Slide 47: 

Fig. 10-5a, p. 158 Meiosis I Stepped Art

Slide 48: 

Fig. 10-5b, p. 159 Meiosis II Stepped Art

10.2-10.3 Key ConceptsStages of Meiosis : 

10.2-10.3 Key ConceptsStages of Meiosis Meiosis reduces the chromosome number Meiosis occurs only in cells set aside for sexual reproduction Meiosis sorts a reproductive cell’s chromosomes into four haploid nuclei, which are distributed to descendent cells by cytoplasmic division

10.4 How Meiosis Introduces Variation in Traits : 

10.4 How Meiosis Introduces Variation in Traits Crossovers and the random sorting of chromosomes in meiosis introduce novel combinations of alleles into gametes, resulting in new combinations of traits among offspring

Crossing Over in Prophase I : 

Crossing Over in Prophase I Crossing over The process by which a chromosome and its homologous partner exchange heritable information in corresponding segments Occurs during condensation in prophase I

Crossing Over Between Homologous Chromosomes : 

Crossing Over Between Homologous Chromosomes

Slide 53: 

Fig. 10-6a, p. 160

Slide 54: 

Fig. 10-6b, p. 160

Slide 55: 

Fig. 10-6b, p. 160 A A a a B Here, we focus on only two genes. One gene has alleles A and a; the other has alleles B and b. B B b b

Slide 56: 

Fig. 10-6c, p. 160

Slide 57: 

Fig. 10-6c, p. 160 C Close contact between the homologous chromosomes promotes crossing over between nonsister chromatids, so paternal and maternal chromatids exchange segments. crossover

Slide 58: 

Fig. 10-6d, p. 160

Slide 59: 

Fig. 10-6d, p. 160 A A a a D Crossing over mixes up paternal and maternal alleles on homologous chromosomes. B b b B

Segregation of Chromosomes into Gametes : 

Segregation of Chromosomes into Gametes Homologous chromosomes can be attached to either spindle pole in prophase I, so each homologue can be packaged into either one of the two new nuclei Random assortment produces 1023 (8,388,608) possible combinations of homologous chromosomes

Random Assortment : 

Random Assortment

Slide 62: 

Fig. 10-7, p. 161 A Alignment in nucleus at metaphase I B Alignments in two nuclei at metaphase II C Nuclei of the four resulting gametes Possible lineup #1 Possible lineup #2 Possible lineup #3 Possible lineup #4

Slide 63: 

Fig. 10-7, p. 161 Stepped Art

10.4 Key Concepts: Chromosome Recombinations and Shufflings : 

10.4 Key Concepts: Chromosome Recombinations and Shufflings During meiosis, each pair of maternal and paternal chromosomes swaps segments Then, each chromosome is randomly segregated into one of the new nuclei Both processes lead to novel combinations of alleles – and traits – among offspring

10.5 From Gametes to Offspring : 

10.5 From Gametes to Offspring Aside from meiosis, the details of gamete formation and fertilization differ among plants and animals

Slide 66: 

Fig. 10-8b, p. 162 mitosis multicelled body (2n) zygote (2n) fertilization DIPLOID meiosis HAPLOID gametes (n) b Animal life cycle

Gamete Formation in Animals : 

Gamete Formation in Animals Males Meiosis of primary spermatocytes produces four haploid spermatids, which mature into sperm Females Meiosis of a primary oocyte forms cells of different sizes; the secondary oocyte gets most of the cytoplasm and matures into an ovum (egg); other cells (polar bodies) get little cytoplasm and degenerate

Slide 68: 

Fig. 10-9, p. 163 sperm (mature, haploid male gametes) secondary spermatocytes (haploid) primary spermatocyte (diploid) diploid male germ cell spermatids (haploid) A Growth B Meiosis I and cytoplasmic division C Meiosis II and cytoplasmic division

Slide 69: 

Fig. 10-9, p. 163 A Growth Stepped Art

Egg Formation in Animals : 

Egg Formation in Animals

Slide 71: 

Fig. 10-10 (left), p. 163 three polar bodies (haploid) first polar body (haploid) oogonium (diploid female germ cell) primary oocyte (diploid) secondary oocyte (haploid) ovum (haploid) A Growth B Meiosis I and cytoplasmic division C Meiosis II and cytoplasmic division

Slide 72: 

Fig. 10-10, p. 163 Stepped Art

More Shufflings at Fertilization : 

More Shufflings at Fertilization Chance combinations of maternal and paternal chromosomes through fertilization produce a unique combination of genetic information Fertilization The fusion of two haploid gametes (sperm and egg) resulting in a diploid zygote

10.5 Key Concepts: Sexual Reproduction in Context of Life Cycles : 

10.5 Key Concepts: Sexual Reproduction in Context of Life Cycles Gametes form by different mechanisms in males and females In most plants, spore formation and other events intervene between meiosis and gamete formation

10.6 Mitosis and Meiosis – An Ancestral Connection? : 

10.6 Mitosis and Meiosis – An Ancestral Connection? Though they have different results, mitosis and meiosis are fundamentally similar processes Meiosis may have evolved by the remodeling of existing mechanisms of mitosis

Slide 76: 

Fig. 10-11c, p. 164 one diploid nucleus two haploid nuclei Prophase I • Chromosomes condense. • Homologous chromosomes pair. Metaphase I Anaphase I Telophase I • Crossovers occur. • Chromosomes align midway between spindle poles. • Homologous chromosomes separate as they are pulled toward spindle poles. • Chromosome clusters arrive at spindle poles. • Bipolar spindle forms; it attaches chromosomes to spindle poles. • New nuclear envelopes form. • Nuclear envelope breaks up. • Chromosomes decondense.

Slide 77: 

Fig. 10-11d, p. 165 two haploid nuclei four haploid nuclei Prophase II Metaphase II Anaphase II Telophase II • Chromosomes condense. • Chromosomes align midway between spindle poles. • Sister chromatids separate as they are pulled toward spindle poles. • Chromosome clusters arrive at spindle poles. • Bipolar spindle forms; it attaches chromosomes to spindle poles. • New nuclear envelopes form. • Nuclear envelope breaks up. • Chromosomes decondense.

10.6 Key ConceptsMitosis and Meiosis Compared : 

10.6 Key ConceptsMitosis and Meiosis Compared Meiosis may have originated by evolutionary remodeling of mechanisms that already existed for mitosis, and before that, for repairing damaged DNA