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Lecture 10

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Western University
Biology 1001A
Tom Haffie

Lecture10: Meiosis List of mechanisms that generate genomic diversity  Unequal crossing over can generate Copy Number Variations (CNV)  Independent assortment  Random fertilizations  Zygotes bring DNA from two different cells into the same cell  Homologous chromosomes carry the same genes, but different alleles  Homologous chromosomes are the same size and the same shape and have the same genes in the same places  Chromosomes never look like how they do in a karyotype in nature  In meiosis I, chromosome number is reduced from diploid to haploid (n)  Reductional division of meiosis  In meiosis II, cells divide to give products with “1xC” amount of DNA  Equational division because the number of chromosomes doesn’t change  Meiosis doesn’t always make gametes -> only in animals  In animal life cycles, the zygote divides by mitosis  In plant life cycles, the zygote and spores divide by mitosis  Doesn’t produce gametes! It produces spores!  They don’t replicate by meiosis, they replicate by mitosis  Multicellular by haploid  Gametophytes make gametes by mitosis  In some fungi/algae, the zygote divides by meiosis  In prophase of meiosis I, replicated homologues pair and recombine  Makes copy number variation  Recombination during meiosis cuts and pastes DNA backbones  Enzymatic process; very highly controlled process  Very similar DNA backbones  Technically, it’s a mutation  Sex isn’t about reproduction, it’s about sexual recombination  Homologues don’t pair side by side, they pair back to back so that all chromatids can participate in recombination  Women do their recombination before they’re born; it happens when they’re a fetus  Meiosis occurs in women before they are born; their egg cells are in meiotic arrest since before they are born  Once they are released once a month, meiosis is complete if they are fertilized, then the meiotic arrest
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