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BIOL 133 (3)
Chapter 3

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BIOL 133
Denise Woodward

Meiosis – why does it happen? • Cell division for reproduction • Diploid cell (2n)  4 haploid cells(1n) – Mitosis: 1(2n)  2(2n) = cloning • Each daughter cell is different from others • Generates genetic diversity Meiosis I • Prophase I • Metaphase I • Anaphase I • Telophase I • Meiosis I: reduces ploidy level and separates homologous chromosomes Homologous chromosomes • Chromosomes w/ same size, shape, and linear arrangement of genes (can have different alleles) Meiosis I: reduction division Meiosis II: equational division Prophase I – What happens? • Chromosomes condense • Homologous chromosomes synapse (attach to each other) • Crossing over can occur Crossing Over • Crossing over produces • genetic diversity When a cell with 2 chromosome pairs goes through meiosis, how many different chromosome arrangements are possible? • 4 possible chromosome arrangements When a cell with 3 chromosome pairs goes through meiosis, how many different chromosome arrangements are possible? • 8 possible chromosome arrangements n # possible arrangements = 2 n=# of homologous pairs Independent Assortment • Metaphase I • Non-homologous chromosomes line up independently of each other After meiosis, gametes mature into sperm and eggs • Where are sperm formed in the human male? • Where are eggs formed in the human female? Spermatogenesis • Spermatogonium (2n): precursor to sperm cells • Spermatogonium  (Mitosis)  primary spermatocyte (2n) • primary spermatocyte  (Meiosis I)  secondary spermatocyte (1n) • secondary spermatocyte (Meiosis II)  spermatid Spermatogenesis • Each spermatid then develops flagella and becomes individual spermatozoa • Sperm are small and do not house many organelles (nucleus and mitochondria) Contains nucleus and acrosome (digestive enzymes to enter egg) Oogenesis • Oogonium (2n): precursor to egg cells • Oogonium  (Mitosis)  primary oocyte (2n) • primary oocyte
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