单选题某植物体细胞内只有一套染色体，所以他是______。 A.单价体 B.单体 C.缺体 D.一倍体

单选题供体菌株为Hfr arg-leu+azirstrs，受体菌株为F-arg+leu-aziRsfrs，为了检出和收集重组体F-arg+leu+aziR，应用下列哪一种培养基可以完成这一任务：______。 A．基本培养基加叠氮化钠 B．基本培养基加叠氮化钠和亮氨酸 C．基本培养基加链霉素 D．基本培养基加链霉素和叠氮化钠

单选题位于X染色体上基因决定的性状______。 A．只表现在雄性个体上 B．只表现在雌性个体上 C．可表现在雄性或雌性个体上 D．与性别无关

单选题与玉米的杂种优势表现没有关系的因素是：______。 A．亲本间的遗传差异 B．亲本的纯合程 C．环境作用 D．亲本芽鞘的颜色

单选题有3个水稻不育系甲、乙、丙，均与各自的恢复系杂交。然后让F1自交，结果发现甲的F2代群体全部散粉，其中一半植株花粉半不育；乙的F2群体分离出不育株和可育株，比例为1:3；丙的F2群体呈现与乙类似的育性分离，但经用大量品种与不育株测交，所有测交组合均发生育性分离；而乙组合的不育后代也用大量品种测交，有的测交组合后代全部植株均不育。哪个不育系与胞质基因无关______。 A．甲 B．乙 C．丙 D．甲和乙

单选题利用一种Hfr菌株和其对应的F-菌株进行中断杂交试验，结果如图所示，图中列出了a、b、c、d、e、f6个位点的转移数，纵轴表示位点的重组率，横轴表示接合的时间，从这些资料看，Hfr菌株的连锁图是______

单选题有一个正反杂交试验，其结果如下：F1均表现母本性状，F3呈3:1分离。则决定其表现型分离的遗传基础是______。 A．父本基因型 B．父本表现型 C．母本基因型 D．母本表现型

单选题当细菌核糖体亚基在CsCl介质中进行离心时，30S和50S亚基分别变为23S和42S亚基，这是由于除去了某些成分所致，被除去的成分是 a．16S rRNA； b．23S rRNA； c．16S rRNA+23S rRNA； d．蛋白质。

单选题在一个有性生殖的自然种群中，除了具有种群大、没有突变发生、没有新基因加入以及个体间的交配是随机的以外，还需具备下列哪一条件，种群的基因库是稳定的( )。

单选题在真核细胞中tRNA的转录是为 a．RNA pol Ⅰ工负责的； b．RNA pol Ⅱ负责的； c．RNA pol Ⅲ负责的； d．不由任何RNA pol负责。

单选题两个植物自交系，它们的种子重量分别为0.2kg和0.4kg，杂交得到的F1种子为0.3kg，F1×F1杂交产生了1024个植株，4株为0.2kg重的种子，4株为0.4kg重的种子，其他植株的种子重量则介于二者中间，由此可估计决定种子重量的基因约为( )对。

单选题用达尔文的自然选择学说，来判断下列叙述中正确的是( )。

单选题两个植物杂交，它们的种子质量分别是0.02kg，杂交得到的F1代的种子都是0.03kg，自交得1000个植株，4株0.018kg的种子，4株是0.04kg，其他植株的种子质量在这两个极端值之间，那么决定种子质量的基因有( )对。

单选题European farm ministers have ended three weeks of negotiations with a deal which they claim represents genuine reform of the common agricultural policy (CAP). Will it be enough to kick off the Doha world trade negotiations? On the face of it, the deal agreed in the early hours of Thursday June 26th looks promising. Most subsidies linked to specific farm products are, at last, to be broken--the idea is to replace these with a direct payment to farmers, .unconnected to particular products. Support prices for several key products, including milk and butter, are to be cut-that should mean European prices eventually falling towards the world market level. Cut-ting the link between subsidy and production was the main objective of proposals put forward by Mr. Fischler, which had formed the starting point for the negotiations. The CAP is hugely unpopular around the world. It subsidizes European farmers to such an extent that they can undercut farmers from poor countries, who also face trade barriers that largely exclude them from the potentially lucrative European market. Farm trade is also a key feature of the Doha round of trade talks, launched under the auspices of the World Trade Organization (WTO) in November 2001. Developing countries have lined up alongside a number of industrial countries to demand an end to the massive subsidies Europe pays its farmers. Several Doha deadlines have already been missed because of the EU's intransigence, and the survival of the talks will be at risk if no progress is made by September, when the world's trade ministers meet in Cancun, Mexico. But now even the French seem to have gone along with the deal hammered out in Luxembourg. Up to a point, anyway. The package of measures gives the green light for the most eager reformers to move fast to implement the changes within their own countries. But there is an escape clause of sorts for the French and other reform-averse nations. They can delay implementation for up to two years. There is also a suggestion that the reforms might not apply where there is a chance that they would lead to a reduction in land under cultivation. These 1et-outs are potentially damaging for Europe's negotiators in the Doha round. They could significantly reduce the cost savings that the reforms might otherwise generate and, in turn, keep European expenditure on farm support unacceptably high by world standards. Mote generally, the escape clauses could undermine the reforms by encouraging the suspicion that the new package will not deliver the changes that its supporters claim Close analysis of what is inevitably a very complicated package might confirm the sceptics' fears.

单选题对于突变与进化的关系，以下哪种说法最正确?( )

单选题Sanger的双脱氧末端终止法DNA序列测定中不需要下列哪种物质?______

单选题在完全显性、独立遗传且无互作情况下，AaBbcc × AabbCc的后代中与A_B_cc表 现型不同的个体比例为