Meiosis

• What process produces gametes?

  Meiosis
• What type of cells are gametes described as?

  Haploid (n)
• Why is the haploid nature of gametes important?

  It restores diploid number during fertilization
• Where does meiosis occur in males?

  In the testes
• Where does meiosis occur in females?

  In the ovaries
• In plants, where does meiosis occur to produce eggs?

  In the ovules
• In plants, where does meiosis occur to produce pollen?

  In the anthers
• How many divisions does meiosis consist of?

  Two divisions
• What happens during interphase before meiosis?

  Chromosomes replicate
• What occurs during Meiosis I?

  Homologous chromosomes separate
• What occurs during Meiosis II?

  Chromatids separate
• What is unique about prophase I of meiosis?

  Homologous pairs form bivalents
• What is the process called when homologous pairs join to form a bivalent?

  Synapsis
• What are points called where non-sister chromatids join during crossing over?

  Chiasmata
• What is the result of crossing over?

  Genetic variation within species
• What happens during prophase I of meiosis?

  1. Bivalent forms and aligns in homologous pairs
  2. Chromosomes condense into chromatids
  3. Nucleus disappears and nuclear envelope breaks down
• What happens during metaphase I?

  Bivalents align at the cell equator

  Centrioles reach the poles and spindle forms
• What contributes to genetic variation during metaphase I?

  Independent assortment of homologous chromosomes
• What happens during anaphase I?

  1. Homologous chromosomes are separated
  2. One chromatid from each pair moves to each pole
  3. Spindle fibres contract to pull chromatids, at the centromere
  4. Haploid number of chromosomes at each pole but still found as chromatids
• How many possibilities exist for independent assortment with 23 chromosomes?

  $2^{23}$ possibilities
• What is the result of anaphase I?

  Haploid number at each pole
• What happens during telophase I?

  1. Nuclear envelope may reform around chromatids
  2. Chromosomes remain condensed
• What occurs during cytokinesis I?

  • Membrane pinches at equator
  • Creates two separate cells
• What is the end result of meiosis I?

  Two daughter cells formed
• How are the daughter cells after meiosis I characterized?

  Haploid and genetically different
• What remains attached at the centromere after meiosis I?

  Chromatids
• Differences in plant cells, in mitosis

  • no centrioles
  • no cell shape change
  • spindle remains