胎儿朝 28 o th i3 i1 88 it se 3 Bi a8 82 ag iaia aa 1 12 14 15 16 x 1 23 (a) normal human male chromosomes XY sex chromosomes sex chromosomes mother posibble sperm possible t possible genoty pes of zygotes (n boxes) possible phenotyp of offspring females males一 胎儿期