BIO 101 Chapter Notes - Chapter 10: Sister Chromatids, Decay Product, Ploidy
Chapter 10: Meiosis
10.1 Sexual Reproduction Produces Genetic Variability
• Makes genetic variability in offspring through union of gametes
o Variation originally created in DNA via mutations
• Fusion of gametes keeps chromosome # constant between generations
• Meiosis reduces chromosome # by half – producing haploid (n) gametes
• Fusion of gametes (fertilization) combines 2 haploid chromosome sets to produce
diploid (2n) zygote
• Diploid – 2 copies of every chromosome per cell
o most of our body cells
o n=46
• Polyploid – more than 2 copies of each chromosome per cell
• Haploid – 1 copy of every chromosome per cell
o Cells in ovaries/testes producing gametes
o n=23
o made by meiosis
10.2 Meiotic Cell Division Produces Genetically Variable Haploid Cells
• Meiotic cell division
o Occurs in animal ovaries and testes
o Meiosis and 2 rounds of cytokinesis
o Produce 4 daughter cells (gametes)
▪ Genetically different from parent cell and each other
▪ Each has ½ genetic info of parent cell
• Key to sexual reproduction in eukaryotic cells
o Diploid cell w/ paired chromosomes produces haploid daughter cells w/
unpaired chromosomes
o Each gamete gets 1 or each pair of homologous chromosomes
• Meiosis I – separates pairs of homologues, each daughter nucleus receiving 1
o Each daughter nucleus is haploid, even though each homologue it receives has 2
chromatids
• Meiosis II – separates chromatids, gives 1 chromatid to each of 2 more daughter nuclei
• Meiosis consists of 1 round of DNA replication and 2 rounds of nuclear divisions
o 1 round of DNA replication produces 2 chromatids in each duplicated
chromosome
o Sister chromatids of each chromosome are attached at centromere
• Prophase I – homologous chromosomes pair up, exchange DNA
o Crossing over – exchange of corresponding chromatid sections (DNA) between
maternal/paternal homologues
▪ Chiasmata – where maternal/paternal chromosomes have exchanged
parts
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