题干

如图为基因组成为Aa的动物在形成精子过程中某一时期示意图.下列对此细胞相关叙述中,正确的是(    )

A:若A在1号染色单体上,2号染色单体上与A相同位置的基因最可能是a

B:若姐妹染色单体没分离,则后代性染色体组成一定为XXY

C:若同源染色体非姐妹染色单体交叉互换将导致染色体结构变异

D:若该动物一个精原细胞产生一个AaaX精子,则同时产生的另外三个精子是AX,Y,Y

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D

同类题4

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

        Both men and women are living longer thesedays in industrialized countries. ____ In general, they can expect to live six or sevenyears more than men. One reason for this is biological.

        One important biological factorthat helps women live longer is the difference in hormones between men and women.____ Between the ages of about 12 and 50, women producehormones that are involved in fertility(生育能力). These hormones also have a positive effect on the heart andblood flow. In fact, women are less likely to have high blood pressure or to diefrom heart attacks.

 

____  Theyhelp the body defend itselfagainst some kinds of infections. This means that women generally get sick lessoften and less seriously than men. The common cold is a good example: women, onaverage, get fewer colds than men.

        ____Scientists are still not exactly sure howinfluence aging, but they believe that they do. Some think that a woman’s body cellshave a tendency(向) to age more slowlythan a man’s. Others think that a man’s body cells have a tendency to age more quickly.____

A. However, women, on average, live longer.

B.The biological factor plays an important part.

C.Women are also helped by their female genes.

D.The female hormones also protect the body in another way.

E.Recent research seems to support both of these possibilities.

F.Therefore, women are more healthy than men and can live a better life.

G.Hormones are chemicals which are produced by the body to control carious body functions.