问题 填空题

已知在正常肤色与白化病这对性状中,白化病是隐性基因控制的(a),正常肤色是显性基因控制的(A).请回答问题:

(1)控制正常肤色的基因组成为______.

(2)一对夫妇均是携带致病基因的正常人,此夫妇结婚后,子女有无患病的可能?______.

(3)一对夫妇,一方的基因组成是Aa,另一方是AA,后代患白化病的可能性是______.

(4)通过(2)(3)的比较,说明都携带白化病基因的夫妇,其后代患遗传病的可能性会______.

答案

由于基因控制生物的性状,由于基因有显性基因和隐性基因,所以性状有显性性状和隐性性状.显性基因用大写字母表示,隐性基因用小写字母表示.

(1)显性性状的基因表示为Aa或AA,隐形性状的基因表示为aa.由于正常肤色是显性性状,所以基因组成为:AA或Aa.

(2)夫妇均是携带致病基因的正常人,所以他们的基因组成均为Aa,基因在亲子代之间的传递图解为:

所以子女有患病的可能.

(3)一对夫妇,一方的基因组成是Aa,另一方是AA,基因在亲子代之间的传递图解为:

,所以后代患病的可能性为0.

(4)通过(2)的图解,一对夫妇均是携带致病基因的正常人,此夫妇结婚后,后代患病的可能性为25%;通过(3)的图解,一对夫妇,一方的基因组成是Aa,另一方是AA,后代患病的可能性为0.说明都携带白化病基因的夫妇,其后代患遗传病的可能性会大.

故答案为:(1)AA或Aa

(2)有可能

(3)0

(4)大

单项选择题
阅读理解

I recently turned fifty,which is young for a tree,midlife for an elephant,and ancient for a sportsman.Fifty is a nice number for the states in the US or for a national speed limit,but it is not a number that I was prepared to have hung on me.Fifty is supposed to be my father’s age,but now I am stuck with this number and everything it means.

A few days ago,a friend tried to cheer me up by saying,“Fifty is what forty used to be.”He had made an inspirational point.Am I over the hill?People keep telling me that the hill has been moved,and I keep telling them that the high-jump bar has dropped from the six feet I once easily cleared to the four feet that is impossible for me now.

“You’re not getting older,you’re getting better,”says Dr.Joyce Brothers.This,however,is the kind of doctor who inspires a second opinion.

And so,as I approach the day when I cannot even jump over the tennis net,I am moved to share some thoughts on aging with you.I am moved to show how aging feels to me physically and mentally.Getting older,of course,is obviously a better change than the one that brings you eulogies(悼词).In fact,a poet named Robert Browning considered it the best change of all:

Grow old along with me!

The best is yet to be.

Whether or not Browning was right,most of my first fifty years have been golden ones,so I will settle for what is ahead being as good as what has gone by.I find myself moving toward what is ahead with a curious blend(混合)of both fighting and accepting my aging,hoping that the philosopher(哲学家)was right when he said.“Old is always fifteen years from now.”

小题1:The author seems to tell us in Paragraph 1 that         .

A.time alone will tell

B.time goes by quickly

C.time will show what is right

D.time makes one forget the past小题2:When the author turned fifty,people around him         .

A.tried to comfort him

B.got inspirations from him

C.were friendlier with him

D.found him more talkative小题3:The author considers his fifty years of life         .

A.peaceful

B.ordinary

C.satisfactory

D.regretful小题4:We can infer from the passage that         .

A.the old should lead a simple life

B.the old should face the fact of aging

C.the old should take more exercise

D.the old should fill themselves with curiosity