问题 读图填空题

牛的毛色有黑色和棕色, 如果两头黑牛交配产生了一头棕色小牛, 回答:

(1)黑色和棕色哪种是显性性状? ____________

(2)如果用B与b表示牛的毛色的显性基因和隐性基因, 写出上述两头黑牛及棕色小牛的基因组成___________.

(3)上述两头黑牛产生一只黑色小牛的可能性是________.

(4)如果用一头雄牛与多头雌牛(基因组成为Bb)交配, 共出生20头小牛, 全部为黑色, 则此雄牛的基因型最可能是_______.

答案

(1)黑色  (2) Bb、Bb、bb   (3)3/4  (4)BB

该题目考查了生物的遗传规律。(1)由题干可知,两头黑牛生出一头棕色小牛,说明发生性状分离,黑色对棕色为显性;(2)其后代为棕色,则基因型为bb,b基因分别来自于其父母双方,二黑牛的基因组成中一定有B基因,所以亲本黑牛的基因组成均为Bb;(3)Bb╳Bb→BB Bb bb 表现型比例为黑色:棕色为3:1,因此该黑牛产下黑色小牛的概率为3/4;(4)雄牛与多头基因型为Bb的雌性杂交,后代共20头,全为黑色,说明雄牛一定为黑色,具有B基因,且所产后代均为黑色,则最可能的基因型为BB。

单项选择题 A1/A2型题
阅读理解

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Are you carrying too much on your back to school? Lots of kids of your age are. Not only are students in China suffering from the problem, but kids in the United States are puzzled by heavy school bags.

Experts are starting to worry that young students are having back and neck problems as a result of school bags being too heavy for them. It is hard for me to get up the stairs with my bag because it's so heavy, said Rick Hammond, an 11-year-old student in the US.

Rick is among the students who have regular backpacks(背包) with two straps (带子) to carry them, but a number of other students choose rolling backpacks. But even with rolling backpacks, getting up stairs and buses with them is still a problem for kids. Many of them have hurt their knees, backs or necks because of heavy school bags.

   But how much is too much? Experts say students should carry no more than 10 to 15 percent of their own body weight. Scott Bautch, a Wisconsin back doctor, said kids under 4th grade should stay with 10 percent, but it’s also important that older kids don’t go beyond (超出) 15 percent, because their bones are still growing.

Bautch explained that there are other injuries caused by backpacks. Kids are losing their balance and falling down with these backpacks, he said.

Parents and teachers are starting to tell kids to only take home library books they will be reading in the evening. Some teachers are using worksheets (作业单 ) or thin workbooks for students to take home.

One of the best answers is, as some kids suggest, to have no homework at all!

60. According to experts, a primary student in Grade 6, who is 40 kilograms, should carry a bag   weighing ______ kilograms at most.

A. 4       B.6       C.8      D.10

61. As school bags are too heavy for younger students to carry, they ______.

A. show no interest in studying at school.

B. often fall ill

C. are having back and neck problems

D. usually ask their parents for help

62. The author wrote the passage to _____.

A. seek(寻找) ways to solve the problem of heavy bags

B. appeal (呼吁) to teachers for caring for the students

C. criticize(批评) the government for having done nothing to help students

D. tell us that heavy bags are bad for students’ health

63. Parents and teachers are starting to tell kids to take home only library books they will be   reading in the evening to ______.

A. make students more interested in reading than watching TV

B. give them more free time to play

C. make their bags easier to carry

D. let them sleep early at night