题目

已知正常的β珠蛋白基因(以βA表示)经Mst I限制酶切割后可得到长度为1． 15kb和o．2kb的两个片段(其中0．2kb的片段通常无法检测到)，异常的β珠蛋白基因(以βS表示)由于突变恰好在Mst I限制酶切割点上，因而失去了该酶切位点，经Mst I限制酶处理后只能形成一个1.35kb的DNA片段，如图l；现用Mst I限制酶对编号为1、2、3的三份样品进行处理，并进行DNA电泳，结果如图2，则1、2、3号样品的基因型分别是(以βA、βS表示相关的基因) A．βSβS、βAβS、βAβA      B． Sally was fourteen．She studied in a middle school．She liked dancing and singing and s __1.____ a lot of time on them．But she hated math and even decided to give it up．Her father was w __2._ about it．It was Sunday．Sally’s father gave a call to his sister who t __3.___ math in another school．He hoped she would come and tell his daughter how to learn math．The woman came and said, “ You are a clever girl, Sally．I’m sure you will soon learn math well if you do your b _4.____．’’“ I’m afraid I can’t , Aunt,” said Sally．“ G __5.____ can’t be good at math ．”“ I don’t think so,” said the woman．“ I was good at it when was a girl．You must do more e _6.____ and try different ways to practice d __7.__ math problems until you work them out or at least understand them better．Here is a math problem．Please think it o ___8.___ and see if you can work it out．”“ Ok,” said the girl．“ Let me try．”About an hour later Sally took the exercise book to her aunt and said, “ I’ve t 9.____ several times and worked out the problem at last!”“ Well done !” her aunt looked at her answer and said h__10.___, “ Now you see, math is not as difficult as you thought．”