单选题家猫中有一位于常染色体上的基因杂合时，呈无尾性状；而在纯合体时，又造成致死结果。当一只无尾猫跟另一只无尾猫杂交时，子代表现型为：______。 A．全部无尾 B．无尾:有尾=3:1 C．无尾:有尾=2:1 D．无尾:有尾=1:2

单选题某染色体各区段的线性顺序是abc.defg，变成了abc.dfeg，这叫______。 A．臂内倒位 B．臂间倒位 C．顺接重复 D．反接重复

单选题减数分裂过程中，实现染色体数目减半是在( )分裂的( )。

单选题无籽西瓜是一个同源三倍体，3n=33。在减数分裂时就可能出现______等不同的联会方式，造成后期工不均衡分离，形成的配子基本上都是不育的。 A．三价体和四价体 B．三价体、二价体和单价体 C．二价体和单价体 D．三价体和单价体

单选题以n题为条件，如果小鼠体重的遗传方差为2.7，那么环境方差约为( )。

单选题锥实螺Dd×Dd，后代为( )。

单选题最早用果蝇为材料发现性连锁遗传的科学家是 ____ ，发现果蝇的X染色体不分离现象并直接证明遗传的染色体学说的科学家是 ____ 。

单选题“生存斗争”是什么的结果?( )

单选题可以通过以下______估算环境变量。 A．F1群体 B．BC1群体 C．BC2群体 D．F2群体

单选题在Hfr×F - 杂交中，染色体转移的起点决定于______。

单选题SRY基因：______。 A．是一种果蝇分节基因，决定体节分化 B．是人类Y染色体短臂上的具有男性性别决定作用的基因 C．是X染色体失活中心的调节基因 D．是哺乳动物性连锁基因剂量补偿效应的开关基因

单选题 用根癌农杆菌作载体转化植物细胞时，不适宜作受体的材料是： A、叶圆片 B、茎切段 C、新分离的原生质体 D、培养2~3天的原生质体

单选题决定紫茉莉花斑遗传的是______。 A.染色体 B.线粒体 C.叶绿体 D.卡巴粒

单选题下列突变哪个属于转换______。 A．A→G B．G→T C．C→G D．T→A

单选题It seemed so promising—mirrors sprawled across desert land in the scorching southwest delivering clean electricity and helping Americans out of the increasing fuel crisis. Some scientists and industry developers claim that Nevada's empty and sun-drenched expanses alone could supply enough electricity to power the entire country. Now even the optimists fear this wonderful prospect may be a mirage. Congress cannot make up their mind to extend the tax-reducing bill for solar-energy projects, which solar advocates say is critical to the future of their industry but which is due to expire at the end of the year. The latest attempt failed in the Senate earlier this month, prospects for a deal before November's presidential and congressional elections now look dim. Uncertainty has led some investors to delay or abandon projects in the past few months. Rhone Resch, the president of the Solar Energy Industries Association, said if the tax-reducing bill is allowed to expire at the end of the year, "it will result in the loss of billions of dollars in new investments in solar. " Further dampening hopes for a big solar-energy boom, the federal Bureau of Land Management (BLM) has abruptly suspended new applications to put solar collectors on federal land. The agency says it has received more than 130 applications and needs to conduct a region-wide environmental impact study on the industry before it will accept any more. The study will take 22 months to complete, however. Few argue against trying to preserve precious water sources and protect desert tortoises and other creatures that might not enjoy cohabiting with sprawling fields of mirrors. But many solar advocates wonder why the government is not acting as cautiously when it comes to drilling for oil and gas. Senator Maria Cantwell, a Democrat from Washington State, wants a congressional probe into the proposed suspension. "The fact that the BLM pops this out without people even knowing about it, especially when solar thermal looks extremely promising as a power source, is not right," she says. Harry Reid of Nevada, who is the majority leader in the Senate, also condemns the BLM's freeze, saying that it could "slow new development to a crawl". The BLM is not without its supporters, however. At a public meeting on June 23rd in Golden, Colorado, Alex Daue, of the Wilderness Society, said that his organization supports renewable energy development as long as it doesn't damage other important resources. The message is clear: no rubber stamps, even for renewable energy.

单选题有关物种的叙述正确的是( )。 ①一个种群就是一个物种；②具有一定的形态结构和生理功能，能相互交配且产生可育后代的一群生物个体；③隔离是新物种形成的必要条件；④在物种形成的过程中，地理隔离和生殖隔离是同时出现的

单选题单基因控制的某一相对性状，其杂合子表现为双亲的中间类型，其可能存在的魁固作用是

单选题人类的白化病是常染色体单基因隐性遗传病，两个都是白化病基因携带者的男女结婚，他们的孩子患白化病的概率是

单选题 下面哪个不是trp操纵子的调控成分？ A、操纵基因 B、前导序列 C、弱化子 D、增强子