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This chapter explores the process of meiosis and sexual reproduction, highlighting the advantages and disadvantages of this life cycle. It investigates the sources of genetic variation and the differences between meiosis and mitosis.
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Question? • Does Like really beget Like? • The offspring will “resemble” the parents, but they may not be “exactly” like them.
Question ? • Do parents give their whole DNA copy to each offspring?
Life Cycle - if Mitosis Female 46 Male 46 egg 46 sperm 46 Zygote 92 mitosis mitosis Mitosis
Life Cycle - if Meiosis Female 46 Male 46 egg 23 sperm 23 Zygote 46 mitosis mitosis Meiosis
MITOSIS MEIOSIS Chiasma (site of crossing over) Parent cell (before chromosome replication) MEIOSIS I Propase Prophase I Chromosome replication Chromosome replication Tetrad formed by synapsis of homologous chromosomes Duplicated chromosome (two sister chromatids) 2n = 6 LE 13-9 Chromosomes positioned at the metaphase plate Tetrads positioned at the metaphase plate Metaphase I Metaphase Anaphase Sister chromatids separate during anaphase Anaphase I Homologues separate during anaphase I; sister chromatids remain together Telophase Telophase I Haploid n = 3 Daughter cells of meiosis I 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II Sister chromatids separate during anaphase II
Anaphase I • .