单选题Any day now, the federal Department of Education will formally propose new regulations that would cut off federal aid to for-profit colleges whose graduates cannot earn enough to repay their student loans. The regulations, known as the "gainful employment" rules, are an effort to rein in the high debt loads students take on when they enroll in for-profit colleges that offer certificates or degrees in fields like nursing or culinary arts. Students at for-profit colleges are much more likely than others to default on their loans. Under the regulations, a draft of which came out in February, for-profit colleges would not be eligible to receive federal student aid if their graduates' debt load was too high to be repaid, over 10 years, with 8 percent of their starting salary. The Career College Association, which represents 1,450 for-profit colleges, is lobbying fiercely against the regulations, which it argues are wrong-headed, unnecessary and likely to restrict needy students' access to vocational training and higher education. With so many community colleges overcrowded, the for-profit colleges say, their programs represent the nation's best hope for training much-needed health care workers and technicians. Arne Duncan, the Secretary of Education, has avoided demonizing the for-profit schools. In a May speech, he said that despite a "few bad apples," for-profit colleges play a vital role in helping the nation reach the Obama administration's goal of having the world's best-educated work force by 2020. Advocacy groups representing students and consumers are less diplomatic. "These programs over-promise, underdeliver and load vulnerable students up with way too much debt," said Chris Lindstrom, higher education program director at the U. S. Public Interest Research Group, part of a coalition of education, consumer, student and public interest groups supporting the regulations. In 2007, coalition members said, students at for-profit colleges made up only 7 percent of those in higher education hut 44 percent of those defaulting on federal student loans. Adding new fuel to the fire was a recent presentation at a New York conference for investors by Steven Eisman, a hedge-fund manager known for having anticipated the housing market crash. Mr. Eisman, whose early awareness of structural problems in the housing market is described in Michael Lewis's bestseller The Big Short, said the for-profit education industry, like the subprime mortgage industry, has rested on the proliferation of loans to low-income people who would not be able to repay them. Federal law has long said that federal student aid can go only to for-profit colleges that "prepare student for gainful employment in a recognized occupation. " But this is the government's first effort to define "gainful employment" in relation to graduates' debt-to-income loads. "With a record number of students attending programs that are subject to this requirement, and a record amount of taxpayer money being used to enable them to attend, it's more important than ever to make sure they're getting their money's worth," said Pauline Abernathy, vice president of the Institute for College Access and Success.

单选题豌豆中红花对白花为完全显性，两株红花植株杂交，其后代产生了白花植株，该白花植株再与红花姊妹株杂交，产生白花植株的概率是(假设没有发生基因突变)

单选题杂合性(具有某杂合型的个体的频率)通常用来测定一个种群的遗传变异。假设一种植物某年的种群数约50个，该年在一个位点上的等位基因频率为p(A)=0.90，q(a)=0.10。下列哪种进化力可能使下一年杂合性提高?

单选题Base-pair substitutions in point mutation include: ______. A．transvertion and transformation B．transition and transvertion C．conversion and transition D．transposition and transvertion

单选题In a strain of fruit fly, after several times of artificial hybridizations, the map distances of the given loci is A-B=10 m.u., A-C=20 m.u., A-D=25 m.u., B-C=30 m.u., B-D=15 m.u., If the genetic map is drawn according to these humbers, the correct locus order should be ______. A．DCBA B．DBAC C．CADB D．ACDB

单选题在研究原核翻译过程中，可用不同的抑制剂研究翻译诸阶段，其中链霉素可抑制 a．起始； b．延长； c．肽基由P位移至A位； d．核糖体移位。

单选题一个Aabb基因型的花粉正常可育株与aaBB基因型的染色体易位株杂交，F1花粉均半不育。则aaBB基因型亲本的染色体结构为______。 A．aaBBTT B．aaBBtt C．aaBBTt D．不一定

单选题在Hfr×F - 杂交中，染色体转移的起点决定于 ____ 。

单选题为了分析某一基因在细胞或组织中的转录水平，可以用来检测mRNA存在的方法是

单选题表观遗传变异(epigenetic variation): ______。 A．在基因的DNA序列不变的情况下，基因表达发生可遗传变异 B．也能引起表型改变 C．包括DNA甲基化、遗传印记、小RNA等造成的可遗传变异 D．上述几项陈述都正确

单选题科学家做了下面的实验：把若干对家蝇分成若干组(每组一对)，再将每组的子代分为A、B两部分，用DDT处理每组的A部分，B部分则不接触DDT(如下表所示)。只选择保留存活率最高的那一组的B部分，A部分及其余各组统统淘汰。将保留的部分再重复这样的实验过程，并且在实验中逐代增加DDT的浓度。经过这样多代的重复，获得了具有很强抗药性的家蝇。上述的实验事实说明( )。 亲代组别 1组(一对蝇) 2组(一对蝇) ……n组(一对蝇) 子代分两份处理 A 施DDT B 无DDT A 施DDT B 无DDT A 施DDT B 无DDT 结果 存活较少 全部存活 存活较多 全部存活 存活很少 全部存活 选择 淘汰 淘汰 淘汰 保留 淘汰 淘汰

单选题生物进化的基础从根本上来自以下哪一过程( )。

单选题某F1个体染色体在减数分裂的终变期出现四体环，造成这种现象的原因是染色体的______。 A．杂易位 B．纯易位 C．杂倒位 D．纯倒位

单选题一个合子有两对同源染色体A和A'及B和B'，在他的生长期间，你预料在体细胞中是下面哪种组合______。 A．AA'BB B．AABB' C．AA'BB' D．AABB E．A'A'B'B'

单选题假设某种二倍体植物A的细胞质在遗传上不同于植物B。为了研究核-质关系，想获得一种植株，这种植株具有A的细胞质，而细胞核却主要是B的基因组，应该怎样做? (a)A×B的后代连续自交；(b)B×A的后代连续自交；(c)A×B后代连续与B回交；(d)A×B的后代连续与A回交；(e)B×A的后代连续与B回交；(f)B×A的后代连续与A回交。

单选题某种氨基酸由二个以上密码进行编码，这种现象是______。 A．简并 B．复制 C．转录 D．翻译

单选题下列关于基因频率的叙述错误的是( )。