题干

动物甲状腺功能有缺陷会导致甲状腺激素分泌不足。有一种耕牛,其甲状腺缺陷可由两种原因引起:一是缺碘,二是一种常染色体上的隐性基因纯合所致。下列有关这种牛的叙述中不正确的是( )

A:缺少甲状腺激素的牛,其双亲可以是正常的

B:甲状腺功能正常的个体,可能具有不同的基因型

C:双方有一方是缺陷者,后代可以出现正常个体

D:甲状腺功能有缺陷的个体,一定具有相同的基因型

上一题 下一题 0.0难度 选择题 更新时间:2014-03-09 03:58:35

答案(点此获取答案解析)

D

同类题4

    Everyone tries to get to school on time. But when bad weather gives you trouble, can you still make it before the bell rings?
In northern China during spring, big sandstorms often make trouble for students and everyone else. When the sky is dark with sand, buses and cars all move much more slowly. Sometimes, people can't even see for 20 metres.
    Sandstorms usually happen in spring. This year, sandstorms started in late March. They have happened in more than 10 provinces (省)  in northern China this year. More than 70 million people have had problems in those places because of the sandstorms.
    People in southern China don't have to worry about this kind of bad weather. Most of the sand comes from Gansu and Inner Mongolia(内蒙古). In northern China, lots of places have few trees and don't get much rain. People there have been cutting down too many trees. When there aren't many trees, the ground can't keep enough water. Over the years, the ground dries up and turns to sand. When spring comes and the ice melts(融化), the ground becomes looser(更松散的). Strong winds take the loose sand into the sky.
    Sandstorms are bad for people's health. If people breathe(呼吸) too much sand, they could cough or have asthma(哮喘).
Sandstorms also give farmers lots of problems. Sometimes their sheep get lost in the storms and never get back home. The winds also tear down farmers' houses.
    What can you do to stop sandstorms? Here’s an idea: Ask you parents to help you plant some trees this spring.
    If you see people cutting down too many trees, tell them about the dangers of sandstorms, and ask your government to stop them from cutting.