Meiosis

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Chapter 10

• Meiosis

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Overview

• Meiosis diploid cell divides to produce 4
  haploid reproductive cells
• Gametes reproductive cells (egg sperm)
• Contains half the number of chromosomes compared
  to somatic cells
• 23 chromosomes instead of 46
• Diploid containing 2 sets of chromosomes
• 2n, such as somatic cells
• Haploid containing 1 set of chromosomes
• 1n, such as gametes

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Steps

• Interphase
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Cytokinesis I
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II
• Cytokinesis II

Meiosis I
Meiosis II
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Why Is Meiosis Special?

• Genetic diversity
• Crossing over or recombination
• Random alignment or independent assortment

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Meiosis I

• Interphase
• Prophase I
• DNA tightly coils into chromosomes
• Spindle fibers appear
• Nucleus and nucleolus disassemble
• Every chromosome lines up with its homologue
• Synapsis pairing of homologous chromosomes
• Tetrad name for each pair of homologous
  chromosomes
• Crossing over exchange of genetic materials
  between maternal and paternal chromosomes
• Genetic recombination new mixture of genetic
  material

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• Metaphase I
• Tetrads line up randomly along the midline of the
  cell
• Spindle fibers attach to the homologous
  chromosomes
• Anaphase I
• Each homologous chromosome moves to an opposite
  pole of the cell
• Independent assortment random separation of the
  homologous chromosome which results in genetic
  variation

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• Telophase I
• Chromosomes reach the opposite ends of the cell
  and cytokinesis I begins

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Meiosis II

• Prophase II
• Spindle fibers form and begin to move chromosomes
  toward the midline of the dividing cell
• Metaphase II
• Chromosomes move to the midline of the dividing
  cell

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• Anaphase II
• Chromatids separate and move toward opposite
  poles of the cell
• Telophase II
• Nuclear membrane forms around the chromosomes in
  each of the four new cells
• Cytokinesis II
• Division of cytoplasm resulting in 4 haploid cells

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Formation of Gametes

• Males
• Testes meiosis is involved in the production of
  male gametes known as sperm cells
• Spermatogenesis production of sperm cells
• Spermatozoa immature sperm cells
• Spermatids a haploid sperm cell
• Results in four haploid sperm cells

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• Females
• Ovaries meiosis involved in the production of
  female gametes known as ova
• Oogenesis production of mature egg cells
• Ovum mature egg cell
• Polar bodies one of three small cells produced
  and discarded during each of the two meiotic
  divisions that yield the haploid egg

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Meiosis I
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Meiosis II