Life on Earth

Chapter 12
Gene Exchange, Meiosis, and Eukaryotic Life Cycles
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Genetic Variability, Genetic Exchange, and the Evolution of Sexual Reproduction
  • Mutations in DNA are the ultimate source of genetic variability.
  • The effects of a mutation depend on the nature of the mutation, the organism in which it occurs, and the environment in which the organism lives.
  • Genetic exchange may combine useful mutations.
  • Eukaryotic organisms use a specialized cell division process called meiosis to combine genetic material from two separate parents in a single offspring.
  • "Permanent" diploidy protects against some of the harmful effects of mutations.

    Meiosis and Sexual Reproduction
  • Meiosis separates homologous chromosomes in a diploid cell to produce haploid daughter cells containing one copy of each type of chromosome.

    The Mechanisms of Meiosis
  • Meiosis I
  • Meiosis II

    Mitosis, Meiosis, and Eukaryotic Life Cycles
  • In haploid life cycles, the majority of the cycle consists of haploid cells.
  • In diploid life cycles, the majority of the cycle consists of diploid cells.
  • In alternation-of-generations life cycles, there are both diploid and haploid multicellular stages.

    The Roles of Meiosis and Sexual Reproduction in Producing Genetic Variability



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