Meiosis

• What does Diploid mean?

  Cellular condition where each chromosome type is represented by only one chromosome
• What does Haploid mean?

  Cellular condition where each chromosome type is represented by one chromosome
• How many division are there in Meiosis?

  2
• What are formed in Meiosis?

  Gametes
• What is the result of Meiosis?

  Genetic Variation
• Stages of Meiosis

  • G2 of interphase
  • DNA replication already occurred
  • Meiosis 1 and 2
• What happens in Meiosis 1?

  Homologous pairs of chromosomes are separated
• What happens in Meiosis 2?

  Sister chromatids are separated
• What happens in Meiosis 1 - Early Prophase?

  • DNA condenses and becomes visible
  • Two chromatids attached at a centromere
  • Centrioles begin to move
  • Nucleolus disappears
• What happens in Meiosis 1 - Mid Prophase?

  • Homologous Chromosomes pair and lie alongside each other (Synapsis)
  • Each pair is called a Bivalent
  • Centrioles move furather towards poles
• What happens in Meiosis 1 - Late Prophase?

  • Chromatids tangle at points called Chiasmata
  • Chromosomes may break and rejoin
  • Crossing over occurs
  • Reformed chromatids called recombinants
• What happens in Meiosis 1 - Metaphase 1?

  • Nuclear Membrane breaks down
  • Spindle forms
  • Bivalents move to the equator and attach to the spindle by the centromere
• What happens in Meiosis 1 - Anaphase 1?

  • Contraction of spindle fibres pulls whole chromosomes towards poles
  • Homologous chromosomes separate
• What happens in Meiosis 1 - Telophase 1?

  • Nuclear membrane reforms around each set of chromosomes
  • Spindle fibres disappear
  • Centrioles divide into two
• What happens in Meiosis 2 - Prophase 2?

  Centrioles move towards opposite poles
• What happens in Meiosis 2 - Metaphase 2?

  • Nuclear membranes disappear
  • Spindles forms at right angles to the first
  • Chromosomes move towards opposite the equator and attach to spindle fibres by centromeres
• What happens in Meiosis 2 - Anaphase 2?

  • Centromeres divide
  • Sister chromatids move towards opposite poles
• What happens in Meiosis 2 - Telophase 2?

  • Each chromatid now called a chromosome
  • Nuclear membrane reforms around each group of chromosomes
  • Spindle fibres disappear and centrioles may divide
• Cytokinesis

  • Division of cytoplasm
  • Four haploid daughter cells are produced
  • Each cell gentically different
• Equation for finding how many pairs can be made from a set of chromosomes

  2$^n$
• Equation for finding the numover of combinations of chromosomes in a zygote

  $2^n\cdot2^n$