问题 选择题

下列说法中不正确的是(  )

A.小明是一个男孩,若他的父母再生一个小孩,则一定是个妹妹

B.表现型是基因型和环境共同作用的结果

C.控制同一性状的不同基因叫等位基因

D.遗传的变异是由于遗传物质的改变而引起的

答案

A、人体细胞内与性别决定有关的染色体叫做性染色体,男性的性染色体是XY,女性的性染色体是XX.当含Y染色体的精子与含X染色体的卵细胞结合形成受精卵时,受精卵将发育成男婴,当含X染色体的精子与含X染色体的卵细胞结合形成受精卵时,受精卵将发育成女孩.由此可见,生男生女决定于生殖过程中卵细胞与哪一种类型的精子相融合.男性产生的两种类型的精子与卵细胞结合的机会是均等的,因此生男生女的几率是一样的,如果小明的父母再生第二胎,是男孩是女孩的几率都是50%,因此不一定是妹妹.故符合题意;

B、表现型是指具有特定基因型的个体,在一定环境条件下,所表现出来的性状特征的总和.基因型相同的个体,在不同的环境条件下,可以显示出不同的表现型.基因型不同的个体,也可以呈现出同样的表现型.例如,杂合子的高茎豌豆基因型为Dd,纯合子的高茎豌豆基因型为DD,但二者均显示出高茎的表现型.因此表现型是基因型与环境共同作用的结果.故不符合题意;

C、位于同一对染色体的相同位置上控制着相对性状的一对基因就是等位基因.故不符合题意;

D、变异是指亲代间和子代个体间的差异,根据变异是否可以遗传,分为可遗传变异和不可遗传变异,遗传物质改变引起的变异属于可遗传的变异,仅由环境因素引起的变异属于不可遗传的变异.故不符合题意.

故选A

阅读理解

INDLANAPOLIS—Doctors and health advocates (提倡者)have warned for years that American children are getting fatter. Now even some kids’ teddy bears are packing on the pounds.

But these heavy toys aim to combat(对抗)obesity, not add to it.

Researchers at Indiana State University in Terre Haute tried a small experiment to test the effects of having kids play with heavier toys. They found that 10 children aged 6 to 8 burned more calories and had higher heart and breathing rate when they moved 3-pound toy blocks instead of unweighted blocks.

So could adding a small weight to stuffed animals and other toys help kids get fit?

“This is not going to solve the obesity problem,” said John Ozmun, a professor who did the study with graduate student Lee Robbins. “But it has been possible to make a positive contribution.”

Some experts cautioned that children could hurt themselves by trying to lift too much too soon and said more activity is preferable to heavier toys. But all agreed that childhood obesity is a big problem.

Obesity rate has become three times over the past 40 years for children and adolescents, raising the risk of diabetes(糖尿病)and other health problems. Federal health officials say more than a third of American children are overweight, and about 17 percent are considered obese(肥胖的).

“Squeezing activity into daily routines can be a good way for children to get more exercise and shed unhealthy pounds,” said Aicia Moag-Stahlberg, who heads Action for Healthy Kids.

“By adding weights, you’re adding some intensity to the action,” she said.

Kara Tucker, youth development coordinator for the National institute for Fitness and Sport in Indianapolis, said active playing helps youngsters work out without realising it.

“Giant soccer is one of my favorites,” Tucker said. “If we told the kids, ‘Hey, you’re going to run up and down the court 20 times,’ they would completely be uninterested. Yet when we put a big soccer ball out there, they will just run forever. They’re having a great time.”

56.What does the passage mainly tell us?

A.American children are getting fatter.

B.New toys are needed for overweight children.

C.Heavier toys help children to combat the obesity problem.

D.Doubts about heavier toys for obese children.

57.What does John Ozmun think of the measure of using heavier toys?

A.It can solve the obesity problem.

B.It is of little use to the obesity problem.

C.It may be of some help to the obesity problem

D.It may hurt children.

58.Some experts think it would be better for obese kids to    .

A.play with light toys

B.play with less heavy toys

C.be on diet

D.have more activity

59.Which of the following is true about obese children in the US?

A.Obesity rate has risen by 30% over the past 40 years.

B.There are now three times as many obese children as 40 years ago.

C.One are fewer overweight children than obese children.

D.There are fewer overweight children than obese children.

60.What Tucker said in the last paragraph suggests that       .

A.he himself likes playing giant soccer balls best

B.he prefers kids to have active playing

C.kids have no interest in running

D.an activity will not work if kids know the purpose of it

判断题