问题 解答题

人有耳垂这种性状是由有耳垂基因决定的,无耳垂这种性状是由无耳垂基因决定的.决定有耳垂的基因(A)是显性基因,决定无耳垂的基因(a)是隐性基因.

(1)人耳垂的有无是一对______.

(2)图中母亲的基因组成是______,女儿的基因组成是______.

(3)图中的女儿成年后与一个基因型为Aa的男子结婚,生出无耳垂孩子的可能性是______%.

答案

(1)同种生物同一性状的不同表现形式称为相对性状.人耳垂的有无,是同一性状的不同表现形式,因此人耳垂的有无是一对是相对性状.

(2)生物体的某些性状是由一对基因控制的,而成对的基因往往有显性和隐性之分,当控制生物性状的一对基因都是显性基因时,显示显性性状;当控制生物性状的基因一个是显性一个是隐性时,显示显性基因控制的显性性状;当控制生物性状的一对基因都是隐性基因,显示隐性性状.决定有耳垂的基因(A)是显性基因,决定无耳垂的基因(a)是隐性基因.因此图中母亲无耳垂的基因组成是aa,女儿的基因组成一个来自母亲,一个来自父亲,因此女儿来自母亲的基因是a,而女儿是有耳垂,因此女儿的基因组成是Aa.

(3)父母双方控制该性状的基因组成都为Aa,表示父母双方的性状是有显性基因A控制,而子女是单眼皮应该是有两个隐性基因aa控制,遗传图解如图:从图解中看出生出无耳垂孩子的可能性是25%.

故答案为:

(1)相对性状         

(2)aa;Aa      

(3)25

改错题
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It was very nice to get your invitation to spend ∧ weekend with you. Luckily
                                       the
I was completely free then, so I’ll to say “yes”. I’ll arrive in Bristol at around 8 p.m.
am
in Friday evening.
on
    Recently,our school has held the meaningful discussion on whether it is reasonable for middle school students to have classes on weekends.Some of our classmates believe we should have classes on weekends.because we can make fully use of the free time to review the lessons we had learnt.Some others are against the opinion,saying we had better to have a good rest on weekends so that we can work effective during the weekdays.The rest agree with neither of the opinion.They have the view which keeping the balance between work and play are both important for us.They suggest one day of the weekend should used to learn our lessons and during the other day they do something interested or have a rest.
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