Chapter 2.3

• Meiosis is the process of cell division that produces gametes. In females, it is the egg made in the ovaries, in males, it is the sperm made in the testes.
• In meiosis, one chromosome from each homologous pair ends up in each gamete (haploid)
• Female sex chromosomes are homologous (XX) where males aren't (XY)
• Steps to meiosis: (First part)

  1. Interphase: DNA from mother cell replicates, chromosomes copy
  2. Prophase I: The homologous pairs link together and they share information (crossing over)
  3. Metaphase I: The homologous pairs line up in the middle of the cell. Spindle fibres form.
  4. Anaphase I: The spindle fibres pull the chromosomes apart
  5. Telophase I: Two new nuclei form
• Steps to Meiosis: (Second part)

  1. Prophase II: Same as prophase I with the 2 new cells
  2. Metaphase II: The chromosomes line up in a single file line (unlike metaphase I)
  3. Anaphase II: The spindle fibres pull the chromatids away from each other
  4. Telophase II: The nuclei form with half the number of chromosomes (23)
• When a single egg and a single sperm fuse, the haploid number of chromosomes turns into a diploid number.
• Independent assortment is when the alleles are randomly distributed on the chromosomes during meiosis
• Non disjunction is the failure of the homologous chromosomes to separate properly during meiosis, causing the cell to have too many or too few chromosomes and leads to some genetic disorders.
• Every gamete that your body makes will be different from every other due to crossing over and independent assortment.