人类遗传病调查中发现两个家系都有甲遗传病(基因为A、a)和乙遗传病(基因为B、b)患者,系谱图如下.若

2025-04-07 09:38:11
推荐回答(1个)
回答(1):

A、Ⅰ-1和Ⅰ-2都不患甲病,但他们有一个患甲病的女儿(Ⅱ-2),说明甲病是常染色体隐性遗传病.A正确;
B、Ⅰ-1和Ⅰ-2都不患乙病,但他们有一个患乙病的儿子(Ⅱ-1),由系谱图可知患乙病的都是男性,所以乙病最可能的遗传方式是伴X染色体隐性遗传,B正确;
C、Ⅰ-1与Ⅰ-2 既不患甲病也不患乙病,但其后代既有患甲病的个体,也有患乙病的个体,因此Ⅰ-2是甲病与乙病致病基因的携带者,基因型为HhXTXt,Ⅱ-5是不患甲病和乙病的男性个体,对甲病来说其基因型是HH或Hh,对于乙病来说基因型是XTY,因此Ⅱ-5的基因型是 HHXTY或HhXTY,故Ⅱ-5的基因型HH或Hh,Hh占

2
3
,同理分析Ⅱ-6的基因型HH或Hh,Hh占
2
3
,因此Ⅱ-5与Ⅱ-6婚配后代患甲病的概率是:aa=
1
4
×
2
3
×
2
3
=
1
9
;再分析乙病,Ⅱ-5的基因型是XTY,Ⅱ-6及其父母正常,但有一患病的兄弟,因此Ⅱ-6的基因型是:XTXT或XTXt,各占
1
2
,因此Ⅱ-5与Ⅱ-6婚配,后代患乙病男孩的概率是XtY=
1
2
×
1
4
=
1
8
,因此如果Ⅱ-5与Ⅱ-6结婚,生一个同时患甲、乙两病男孩的概率为
1
8
×
1
9
=
1
72
,C错误;
D、③Ⅱ-7为Hh的几率是
2
3
,Ⅱ-8为Hh的几率是10-4,则他们再生一个女儿患甲病的概率为
2
3
×10-4×
1
4
=
1
60000
,D正确.
故选:C.

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