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Meiosis. Mitosis vs. Meiosis. Meiosis. 1 replication of chromosomes, in interphase , followed by 2 cell divisions Occurs in plants and animals that reproduce sexually Usually occurs in specialized sex organs – ovaries and testes. Mieosis. Gametes –

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meiosis1
Meiosis
  • 1 replication of chromosomes, in interphase, followed by 2 cell divisions
  • Occurs in plants and animals that reproduce sexually
  • Usually occurs in specialized sex organs – ovaries and testes
mieosis
Mieosis
  • Gametes –
    • Specialized cells that participate in sexual reproduction
    • Sperm and egg
homologous chromosomes
Homologous Chromosomes
  • Pair of chromosomes that are the same length and shape
  • Carry the same types of genes
  • Humans get one from each parent
counting chromosomes
Counting Chromosomes
  • Humans have 23 types of chromosomes
    • One of each type from each parent gamete
    • 23 (mom) + 23 (dad) = 46 total chromosomes
      • This is the Diploid (2n) number
      • Diploid – 2 chromosomes, one homologous pair
      • In humans 2n = 46
counting chromosomes1
Counting Chromosomes
  • Gametes have only one set of chromosomes
  • Haploid (n) – 1 chromosome from a homologous pair
  • In humans n = 23
stages of meiosis
Stages of Meiosis
  • Both parts follow similar pattern
    • Prophase
    • Metaphase
    • Anaphase
    • Telophase
    • Cytokinesis
  • Very similar to mitosis
    • Two parts –
    • Meiosis I
    • Meiosis II
interphase i
Interphase I
  • Same as in mitosis
    • Chromatin replicate
    • Cell growth
prophase i
Prophase I
  • Chromosomes form
  • Homologous pairs come together
  • Crossing over occurs
  • Nuclear membrane starts to dissapate
metaphase i
Metaphase I
  • Homologs move to the equator or metaphase plate
anaphase i
Anaphase I
  • Homologs are separated and one from each pair moves toward opposite ends of the cell
telophase i and cytokinesis
Telophase I and Cytokinesis
  • Chromosomes uncoil
  • Nuclear membrane reforms
  • Spindle fibers break down
  • Two daughter cells form
    • These cells are haploid
      • Only have one of each type of chromosome
meiosis ii
Meiosis II
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II
  • Happens simultaneously in both daughter cells
  • No interphase –
    • Chromosomes are already duplicated
  • Same as Mitosis
meiosis differences
Meiosis Differences
  • Female –
    • Form one gamete during meiosis
    • Other three cells are broken down
  • Male –
    • form four gametes during meiosis