题干

某种鱼的鳞片有4种表现型:单列鳞、野生型鳞、无鳞和散鳞,由两对同源染色体上的两对等位基因(分别用Aa、Bb表示)决定,且BB对生物个体有致死作用。将无鳞鱼和纯合野生型鳞的鱼杂交,F1有两种表现型,野生型鳞的鱼占50%,单列鳞鱼占50%;选取其中的单列鳞鱼互交,其后代有上述4种表现型且比例为6:3:2:1,则F1的亲本基因型组合是()

A:aaBb×AAbb或aaBB×AA

B:AABb×aa

C:aaBb×AA

D:AaBB×Aa

上一题 下一题 0.0难度 选择题 更新时间:2017-05-05 09:54:35

答案(点此获取答案解析)

C

同类题3

任务型阅读,阅读下列短文,根据短中的信息完成文后表格。(每空一词)

    Have you ever been so worried about something that you have a headache or even can't sleep at night? Then you cannot pay enough attention during a test or in your study. If so, then you know that is stress. You are worried too much about something. The bad feeling in your mind can make you angry, sad, or scared, and can even give you a stomachache or a headache.

    However, some kind of stress is good. You might feel excited when you are called to give a speech at school. You feel nervous but excited. This kind of stress can help you to get things well done. And you may do a better job in your test if the stress pushes you to prepare more beforehand(提前).

    On the other hand, bad stress can last long if you are unable to come over your problems. You may not feel well, if your parents are having a quarrel, if a family member is badly ill, if you're doing poorly at school, or if anything else makes you unhappy. That kind of stress isn't going to help you. And it can actually let you do worse in your daily life.

    The best way to fight the stress is to have a balanced life. Make sure you get enough sleep and eat properly. Have some regular exercise. You should take some time for fun. Get advice from your parents, teachers and friends. Soon after that, you'll probably get away with your stress.

Title:  Face the ____

Meaning of stress

Stress is a feeling if you ____ too much about something that you cannot solve.

Possible effect

You may feel ____ in your mind and body.

Different

kinds

Good stress

•You might feel ____ when you speak in public.

•You will do the job well.

•It makes you ____ more  before doing an important job.

 ____ stress

Stress can last long if you are ____ to come over your problems. It can actually let you do ____  in your daily life.

How to keep stress away

Keep a ____ life in mind. They are sleep, ____ , exercise, time for fun and talk with others.