Early development

Summary of Section 4

  1. Gametes are special cells because they contain only one set of chromosomes instead of the more usual two sets.
  2. The chromosome number is halved by meiosis.
  3. The crossing over and random assortment of chromosomes in meiosis produces a unique set of genes in every gamete, and thus in every individual (except for identical twins, who are derived from the same conceptus).
  4. Sperm production involves many rounds of mitosis, one meiosis (involving two cell divisions), and a maturation and packaging phase. Millions of sperm can be produced every day.
  5. Egg production also involves mitosis followed by meiosis, but the meiosis is arrested until the oocyte is stimulated to re-enter division. Only one egg is produced per menstrual cycle, and only one gamete is produced as a result of each meiosis.
  6. Gamete production in both men and women is infuenced by hormones.
  7. Good health is necessary for the production of healthy gametes.