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Chapter 13 Meiosis and Sexual Life Cycles Chapter 13 Meiosis and Sexual Life Cycles Each gene has a specific location on a specific chromosome. Chapter 13 Meiosis and Sexual Life Cycles We inherit one set of chromosomes from our father and one set from our mother. Chapter 13 Meiosis and Sexual Life Cycles Asexual Sexual Chapter 13 Meiosis and Sexual Life Cycles Asexual reproduction produces genetically identical offspring by mitosis. Sexual reproduction forms genetically diverse offspring. Chapter 13 Meiosis and Sexual Life Cycles In humans, 2n = 46 n = 23 Chapter 13 Meiosis and Sexual Life Cycles In humans, 2n = 46 n = 23 22 pairs are homologous, the 23rd pair is either XX or XY. Chapter 13 Meiosis and Sexual Life Cycles Gonads (testes and ovaries) produce haploid gametes by meiosis Chapter 13 Meiosis and Sexual Life Cycles Gonads (testes and ovaries) produce haploid gametes by meiosis. Sperm and ovum unite to form a diploid zygote, which grows and develops by mitosis. Chapter 13 Meiosis and Sexual Life Cycles Sexual life cycles differ in the timing of meiosis in relation to fertilization Chapter 13 Meiosis and Sexual Life Cycles Sexual life cycles differ in the timing of meiosis in relation to fertilization. Multicellular organisms may be diploid or haploid or may alternate between haploid and diploid generations. Chapter 13 Meiosis and Sexual Life Cycles Meiosis differs from mitosis in three ways: 1. Synapsis 2. Crossing over 3. Separating homologous pairs (not sister chromatids) during anaphase I. Chapter 13 Meiosis and Sexual Life Cycles Chapter 13 Meiosis and Sexual Life Cycles Chapter 13 Meiosis and Sexual Life Cycles Chapter 13 Meiosis and Sexual Life Cycles Chapter 13 Meiosis and Sexual Life Cycles Genetic variation is the raw material for evolution Chapter 13 Meiosis and Sexual Life Cycles Genetic variation is the raw material for evolution. Mutations create variation Chapter 13 Meiosis and Sexual Life Cycles Genetic variation is the raw material for evolution. Mutations create variation. Sexual reproduction promotes variation. Chapter 13 Meiosis and Sexual Life Cycles Sexual reproduction promotes variation three ways: 1. Independent assortment of chromosomes during meiosis 2. Crossing over during metaphase I 3. Random fertilization of egg cells by sperm. Concept Check Questions Offspring acquire genes from parents by inheriting chromosomes • How are the traits of parents (such as hair color) transmitted to their offspring? Concept Check Questions Offspring acquire genes from parents by inheriting chromosomes • In the absence of mutation, asexually reproducing organisms produce offspring that are genetically identical to each other and to their parents. Explain. Concept Check Questions Offspring acquire genes from parents by inheriting chromosomes • In organisms that reproduced sexually, how similar are the offspring to their parents? Explain. Concept Check Questions Fertilization and meiosis alternate in sexual life cycles • How does the karyotype of a human female differ from that of a human male? Concept Check Questions Fertilization and meiosis alternate in sexual life cycles • How does the alternation of meiosis and fertilization in the life cycles of sexually reproducing organisms maintain the normal chromosome count for each species? Concept Check Questions Fertilization and meiosis alternate in sexual life cycles • Dog sperm contain 39 chromosomes. What are the haploid number and diploid number for dogs? Concept Check Questions Fertilization and meiosis alternate in sexual life cycles • What process (meiosis or mitosis) is more directly involved in the production of gametes in animals? In plants and most fungi? Concept Check Questions Meiosis reduces the number of chromosome sets from diploid to haploid • Using the concept of chromosome sets, explain briefly how mitosis conserves chromosome number, whereas meiosis reduces the number of chromosomes by half. Concept Check Questions Meiosis reduces the number of chromosome sets from diploid to haploid • How are the chromosomes in a cell at metaphase of mitosis similar to and different from the chromosomes in a cell at metaphase of meiosis II? Concept Check Questions Genetic variation produced in sexual life cycles contributes to evolution • Fruit flies have a diploid number of 8, and honeybees have a diploid number of 32. Assuming no crossing over, is the genetic variation among offspring from the same two parents likely to be greater in fruit flies or in honeybees? Explain. Concept Check Questions Genetic variation produced in sexual life cycles contributes to evolution • Under what circumstances would crossing over during meiosis not contribute to genetic variation among daughter cells?