题目内容

【题目】家兔的黑色和褐色是一对相对性状。现有甲、乙、丙、丁4只家兔，其中甲、乙是雌兔，丙和丁是雄兔。甲、乙、丙全为黑色，丁为褐色。已知甲和丁交配的后代全部是黑色子兔，乙和丁交配的后代有褐色子兔。请回答下列问题：

（1）黑色和褐色这两种体色中，显性的是 色。

（2）甲、乙、丁三只兔的遗传因子组成分别是（用F、f表示）

甲： ；

乙： ；

丁： ；

（3）如何鉴别丙兔是纯合子还是杂合子？

【答案】

（1）黑

（2）FF Ff ff

（3）丙与乙杂交，若后代出现褐色，说明丙是杂合子；若后代全是黑色，说明丙是纯合子

【解析】

（1）甲兔与丁兔交配的后代全部为黑色子兔，无性状分离，即可判断黑色是显性性状，褐色是隐性性状。

（2）根据上面的分析，甲和丁的子代无性状分离，说明甲兔是显性纯合子，遗传因子组成为FF，丁兔是隐性个体，遗传因子组成为ff；而乙和丁交配的后代中有性状分离现象，所以乙是杂合子，遗传因子组成为Ff。

（3）因为丙是雄兔，而在甲、乙两雌兔中无隐性个体，所以只能让丙与乙交配来鉴别其遗传因子组成。如果交配后得到的子代全部是黑色子兔，说明丙是纯合子，遗传因子组成为FF；如果交配后得到的子代中有隐性个体褐色子兔出现，则丙是杂合子，遗传因子组成为Ff。

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