单选题哪一种形式的自然选择可以导致种的分化和多形现象?( )
单选题双螺旋DNA有A型、B型、C型以及Z型等结构形式，在正常生理条件下占优势的形式是
a．A型； b．B型； c．C型； d．Z型。
单选题生物的适应是( )。
单选题细菌中丧失合成某种营养物质能力的突变型，称为______。
A.营养缺陷型
B.原养型
C.野生型
D.接合型
单选题RNA并接需要snRNP的协助，其中能识别左端(5′)拼接点共有序列的snRNP是
a．U1 snRNP； b．U2 snRNP； c．U5 snRNP； d．U2 snRNP+U5 snRNP。
单选题达尔文的进化理论不能解释的问题是( )。 ①生物的多样性；②保护色；③生物遗传和变异的性质；④变异的不定向和选择的定向；⑤自然选择对遗传和变异如何起作用；⑥生物的生存斗争
单选题以下关于F因子的叙述不正确的是______。 A．F+通过性伞毛与F-结合，传递F因子 B．F-得到F因子变成F+，F+失去F因子变成F- C．F因子在F+细胞内以两种形式存在，游离于细胞质中或整合在细菌染色体上 D．F+和F-杂交通常指转移F因子，染色体上基因转移的频率很小，不到10-6
单选题The vector of sexduction is______． A．the chromosome of a high frequency recombination bacterium B．an episome of a conjugated bacterium C．the episome of F' bacterium D．F factor or a transductable bacteriophage
单选题As Philadelphia grew from a small town into a city in the first half of the eighteenth century, it became an increasingly important marketing center for a vast agricultural hinterland. Market days (1) the crowded city even more crowded, as farmers from within a (2) of 24 or more kilometers brought their sheep, vegetables, cider and other products for direct sale to the (3) . The High Street Market was continuously (4) throughout the period until 1736, (5) it (6) from Front Street to Third. By 1745 New Market was opened on Second Street. The next year the Callow Hill Market began (7) . Along with market days, the (8) of twice-yearly fairs persisted in Philadelphia (9) after similar trading days had been discontinued in other colonial cities. The (10) provided a means of bringing handmade goods from (11) places to would-be buyers in the city. Linens and stockings from Germantown, (12) , were popular items. Auctions were another popular (13) of trade. Because of the competition, retail (14) opposed these as well as the fairs. (15) governmental attempts to eradicate fairs and auctions were less than successful, the ordinary (16) of economic development was on the merchants'side, as increasing business specialization became the (17) of the day. Export merchants became differentiated from their importing counterparts, and specialty shops began to appear (18) general stores selling a variety of goods. One of the reasons Philadelphia's merchants prospered was because the surrounding area was undergoing tremendous economic and demographic growth. They did their business, (19) , in the capital city of the province, (20) to not only the governor and his circle, but citizens from all over the colony.
单选题Grifith利用R和S型肺炎球菌所做的工作说明______
A.从死亡的菌体内得到的遗传物质，可转化到活细菌中去
B.DNA是遗传物质
C.DNA是双链分子
D.蛋白质合成是由DNA控制的
单选题某校共有学生1600人，色盲遗传病调查研究后发现，该群体中色盲基因的频率是6.8%，780名女生中有患者23人、携带者52人，男生中色盲的人数约为( )。
单选题Education is one of the key words of our time. A man, without an education, many of us believe, is an unfortunate victim of unfortunate circumstances deprived of one of the greatest twentieth-century opportunities. Convinced of the importance of education, modern states "invest" in institutions of learning to get back "interest" in the form of a large group of enlightened young men and women who are potential leaders. Education, with its cycles of instruction so carefully worked out, is punctuated by textbooks--those purchasable wells of wisdom what would civilization be like without its benefits? So much is certain: that we would have doctors and preachers, lawyers and defendants, marriages and births; but our spiritual outlook would be different. We would lay less stress on "facts and figures" and more on a good memory, on applied psychology, and on the capacity of a man to get along with his fellow-citizens. If our educational system were fashioned after its bookless past we would have the most democratic form of "college" imaginable. Among the people whom we like to call savages all knowledge inherited by tradition is shared by all; it is taught to every member of the tribe so that in this respect everybody is equally equipped for life. It is the ideal condition of the "equal start" which only our most progressive forms of modern education try to reach again. In primitive cultures the obligation to seek and to receive the traditional instruction is binding on all. There are no "illiterates"--if the term can be applied to peoples without a script--while our own compulsory school attendance became law in Germany in 1642, in France in 1806, and in England in 1976, and is still non-existent in a number of "civilized" nations. This shows how long it was before we considered it necessary to make sure that all our children could share in the knowledge accumulated by the "happy few" during the past centuries. Education in the wilderness is not a matter of monetary means. All are entitled to an equal start. There is none of the hurry that, in our society, often hampers the fui1 development of a growing personality. There, a child grows up under the ever-present attention of his parents; therefore the jungles and the savages know of no "juvenile delinquency". No necessity of making a living away from home results in neglect of children, and no father is confronted with his inability to '"buy" an education for his child.
单选题在某项实验中，处于反式位置的a1和a2突变并不互补，不表现出野生型，而b1和b2却能发生互补。______。 A．a1和a2，b1和b2在同一顺反子中，是等位基因。 B．a1和a2是同一顺反子，是等位的，b1和b2不在同一顺反子，是非等位基因。 C．a1和a2不在同一顺反子，是非等位的，b1和b2在同一顺反子，是等位基因。 D．a1和a2，b1和b2都不在同一顺反子，是非等位基因。
单选题DNA分子可以呈超螺旋型和松散型，两者都具有一定的自由能
a．螺旋型具有较高的自由能； b．松散型具有较高的自由能；
c．两者所具有的自由能大体相等。
单选题增强子(enhancer)与启动子的不同在于
a．增强子与转录启动无任何关系；
b．增强子包含数个功能单元(module elements)，而启动子则只有一个单元；
c．启动子可位于起始点的上游，而增强子只能位于起始点的下游；
d．增强子可能位于上游和下游，但不靠近起始点。
单选题遗传漂变可以发生在
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