在果蝇中,隐性基因 s 引起黑色身体,另外一个隐性基因 t 能抑制黑色基因的表 现,所以果蝇是正常灰色。如此,基因型 ssT -是黑色,其余皆为正常灰色。那么 SsTt × ssTt 杂交后代的表现型及其比例为 ( ) 。
A.
正常灰色 : 黑色=1:1
B.
3 / 8 正常灰色 : 5 / 8 黑色
C.
5 / 8 正常灰色 : 3 / 8 黑色
D.
不确定
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