Biolog 10 - Chapter 10: Meiosis and Sexual Reproduction A....

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Chapter 10: Meiosis and Sexual Reproduction A. Alleles and reproduction Each parent donates genes to their offspring via sexual reproduction. The genes combine to give different but similar looking offspring. Asexual reproduction—No males are needed, all individuals can produce offspring. Sexual reproduction—Only females can produce offspring, therefore fewer are produced. B. Meiosis Reduces the chromosome number by half, sexual recombination occurs. Meiosis of diploid cells produces haploid daughter cells function as gametes Gametes undergo fertilization to restore diploid number of chromosomes in zygote Meiosis and fertilization introduce genetic variation in three ways: 1. Crossing over between homologous chromosomes at prophase I. 2. Independent assortment of homologous pairs at metaphase I: Each homologous pair can orient in either of two ways at the plane of cell division. The total number of possible outcomes = 2n (n = number of haploid chromosomes). 3. Random chance fertilization between any one female gamete with any other male Meiosis I and Meiosis II, resulting in four daughter cells. 1. The first division, meiosis I, separates homologous chromosomes. 2. The second, meiosis II, separates sister chromatids. Meiosis I is preceded by interphase where chromosomes are replicated to form sister chromatids. Prophase I occupies more than 90% of the time required for meiosis. Chromosomes begin to condense. Homologous chromosomes pair up in synapsis in a four group (tetrad) where the arms of chromosomes in a homologous pair become break off and switch places. (crossing over) Metaphase I , the tetrads are all arranged at the metaphase plate, with one
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This note was uploaded on 12/03/2011 for the course CHEM BIO P 101 taught by Professor Kk during the Spring '11 term at Rochester.

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Biolog 10 - Chapter 10: Meiosis and Sexual Reproduction A....

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