题目

以下有关基因重组的叙述，正确的是（ ）A.非同源染色体之间互换片段不属于基因重组B.同源染色体的姐妹染色单体间对应片段的交换导致基因重组C.雌雄配子的随机结合产生多种类型的后代属于基因重组D.同卵双生兄弟间的性状差异是基因重组导致的 答案：【答案】A【解析】基因重组：1、概念：在生物体进行有性生殖的过程中，控制不同性状的非等位基因重新组合。2、类型：（1）自由组合型：减数第一次分裂后期，随着非同源染色体自由组合，非同源染色体上的非等位基因也自由组合；（2）交叉互换型：减数第一次分裂前期（四分体），基因随着同完形填空． 　　It is very difficult for a young person to decide what he will 1 . Some people know that they 2 doctors, teachers or workers when they are 3 six years old. But 4 of us will have no 5 about an occupation 6 someone or something makes us 7 the problem. 　　Choosing an occupation 8 time, and you have to 9 a lot of things 10 you try to decide what you would like to do. You may find that you will have to 11 special lessons for 12 work, or 13 you will 14 to get some experience and knowledge for a job. 　　Fortunately, you can ask a lot of people 15 advice and help when you are doing 16 . At most schools, there are teachers to give you 17 on jobs. And you can talk 18 your ideas with family members and friends. It is 19 to make the decision yourself 20 other people can help you with it. 1． [　　] A．doB．make C．getD．give 2． [　　] A．must beB．will be C．have to beD．want to be 3． [　　] A．alreadyB．only C．stillD．even 4． [　　] A．someB．few C．mostD．one 5． [　　] A．problemB．matter C．wayD．idea 6． [　　] A．whenB．until C．sinceD．after 7． [　　] A．faceB．think C．findD．know 8． [　　] A．usesB．spends C．takesD．wastes 9． [　　] A．think aboutB．talk about C．wait forD．look for 10． [　　] A．becauseB．once C．whileD．as 11． [　　] A．teachB．hear C．haveD．know 12． [　　] A．a piece ofB．a kind of C．a bit ofD．a lot of 13． [　　] A．howB．why C．thatD．/ 14． [　　] A．agreeB．like C．decideD．need 15． [　　] A．aboutB．for C．toD．on 16． [　　] A．itB．this C．soD．such 17． [　　] A．adviceB．help C．booksD．lessons 18． [　　] A．overB．under C．withD．without 19． [　　] A．difficultB．useful C．possibleD．important 20． [　　] A．ifB．though C．andD．but