A.50% B.100% C.25% D.75%
A.XBXb B.XBXB C.XbXb D.XBY
A.精子和卵細(xì)胞形成時(shí) B.減數(shù)分裂時(shí) C.胚胎發(fā)育時(shí) D.受精卵形成時(shí)