تجربة

Sexual reproduction occurs when female and male gametes (oocyte and spermatozoon, respectively)

unite at fertilization. Gametes are direct descendants of primordial germ cells, which are

first observed in the wall of the yolk sac at week 4 of embryonic development and subsequently

migrate into the future gonad region. Gametes are produced by gametogenesis (called oogenesis

in the female and spermatogenesis in the male). Gametogenesis employs a specialized

process of cell division, meiosis, which uniquely distributes chromosomes among gametes