果蝇经射线辐射处理后，其X染色体上可发生隐性突变，基因纯合时_爱下问搜题

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问题单项选择题

果蝇经射线辐射处理后，其X染色体上可发生隐性突变，基因纯合时可以引起胚胎致死（根据隐性纯合子的死亡率，隐性致死突变分为完全致死突变和不完全致死突变）。将经射线辐射后的一只雄果蝇与野生型纯合雌果蝇交配得到F1，将Fl单对交配，分别饲养，根据F2的表现型及比例推测待测果蝇的变异情况（如下图所示）。下列说法不正确的是（）

A.若不发生突变，则F2中雄蝇无隐性突变体

B.若发生隐性突变，则F2中显性性状：隐性性状=3：1

C.若发生隐性完全致死突变，则F2中雌：雄＝2：1

D.若发生隐性不完全致死突变，则F2中雌：雄介于1：1和2：1之间

答案

参考答案：B

解析：

若不发生突变，待测果蝇的基因型为XBY，则F2中雄蝇的基因型均为XBY，无隐性突变体，A项正确；若发生隐性突变，待测果蝇的基因型为XbY，则F1的基因型为XBXb、XBY，F2的基因型为XBXB、XBXb、XBY、XbY，其中XbY可引起胚胎致死，若为完全致死突变，则F2中雌：雄＝2：1，若为不完全致死突变，则F2中雌：雄介于1：1和2：1之间，无论哪一种隐性致死突变，F2中显性性状与隐性性状的比例不可能为3：1，B项错误，C、D两项均正确。

考点：本题考查基因的分离定律、伴性遗传的相关知识，意在考查学生能理解所学知识的要点，把握知识间的内在联系，能运用所学知识与观点，通过运用比较、分析与综合等方法对某些生物学问题进行解释、推理，做出合理判断或得出正确结论的能力。

完形填空

When I walked into McCarley’s Bookstore in Ashland, Ore, I began to scan titles on the shelves. The man behind the counter, Mac McCarley, asked if I’d like         . I said yes because I needed to         for college.
I worked after school and during summers, and the job helped pay for my freshman year of college. I would work many other jobs: I made coffee in the Students’ Union         college and even made maps for the US Forest Service. But selling books was one of the most
One day a woman asked me for         on cancer. She seemed fearful. I showed her everything we had in         and found other books we could         . She left the store         , and I’ve always remembered the         I felt in having helped her.
Years later, as a         in Los Angeles, I heard about an immigrant （移民）child who was born with his thumb attached, weblike, to the rest of his hands. His family couldn’t         a corrective operation, and the boy lived in         , hiding his hand in his pocket. I
   my boss to let me do the             . After my story was broadcast, a doctor and a nurse called,         to perform the operation for free.
I visited the boy in the recovery room after the operation. The first thing he did was hold up his         hand and said , “Thank you.” I felt a sense of reward.
At McCarley’s Bookstore I always sensed I was working for the         , not the store. Today it’s        . NBC News pays my salary, but I feel as if I work for the        , through my “Today” show, helping them make        of the world.

A．gain experience

B．start saving

C．get a degree

A．much happier

B．less anxious

C．less disappointed

D．more confident

C．TV reporter

小题14: A. story B operation C. thing D. favor

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