题目

已知番茄的红果（R）对黄果(r)为显性，高茎（D）对矮茎（d）为显性，这两对基因独立遗传。某一红果高茎番茄测交，对其后代再测交。下图为第二次测交后代中各种表现型的比例。最先用来做实验的亲本红果高茎番茄植株的基因型是（ ）A. RRDd B. RRDDC. RrDD D. RrDd 答案：【答案】A【解析】图中红果：黄果=1：1，矮茎：高茎=3：1，由此推测第二次测交亲本的基因型，据此答题。根据图中的数据（1）红果：黄果=1：1，说明第二次测交亲本的基因型是Rr；即第一次测交产生的子代是Rr，则第一次测交的亲本是RR；（2）矮茎：高茎=3：1，说明第二次测交亲本的基因型是dd、Dd，阅读下面短文内容，从题中所给的A、B、C、D四个选项中选出最佳选项。Mrs. Black is such a heavy woman in the world that one day she goes to see the doctor.The doctor tells her that she should eat more vegetables and less meat. So the next morning she only has an egg and a glass of milk for breakfast. And she has some rice and vegetables for lunch.In the evening, she feels very hungry. She begins to cook supper. She makes some hamburgers with chicken. She puts a little chicken and lots of vegetables in each hamburger. She has five hamburgers for supper. After that, she feels better and goes to bed. After a week, she goes to see the doctor again. The doctor is so surprised to find that she is heavier. But Mrs. Black tells him that she has more vegetables and less meat every day! 【1】Why does Mrs. Black go to see the doctor?A. Because she has a cold. B. Because she can’t eat meat.C. Because she can’t sleep well. D. Because she is too fat.【2】What does Mrs. Black have for breakfast?A. Chicken. B. An egg and some milk. C. Rice and vegetables. D. Hamburgers.【3】What does Mrs. Black put in each hamburger?A. A lot of chicken. B. A few vegetables. C. A lot of meat. D. A little chicken and a lot of vegetables.【4】Which of the following food is not mentioned (提及) in the passage?A. Milk. B. Vegetables. C. Ice cream. D. Chicken.【5】Why is Mrs. Black heavier?A. Because she eats too much.B. Because she eats eggs.C. Because she eats a lot of meat. D. Because she eats more meat and less vegetables.