单选题真核细胞的染色质主要是由以下______成分构成的。

单选题在独立遗传下，杂种AaBbDdEe自交，后代中基因型全部纯合的个体占______。 A．25% B．1/8 C．1/16 D．9/64

单选题正反交结果一致的遗传方式有 ____ 。

单选题人工选择之所以能选育出新品种，自然选择之所以能形成新物种，其共同的选择基础是( )。

单选题某人是一个常染色体基因的杂合子Bb，而他带有一个隐性的X连锁基因d。在他的精子中有多大比例带有bd基因? (a)0； (b)1/2； (c)1/8； (d)1/16； (e)1/4。

单选题______可以促进非严格配对的两段DNA发生重组。

单选题细菌杂交实验中，F因子和部分细菌染色体转移频率都比较高的杂交组合是______。

单选题Back in the 1870s, Charles Darwin's cousin Francis Galeton wanted to define the face of a criminal. He assembled photographs of men convicted of heinous crimes and made a composite by lining them up on a single photographic plate. The surprise: everybody liked the villain, including Galton himself. He reasoned that the villainous irregularities he supposed belonged to criminal faces had disappeared in the averaging process. In the next century, scientists began to show reliably that faces combined digitally on computers were likable—more so than the individual faces from which they were composed. Although people clearly admire the long legs of Brazilian model Ana Hickmann or Dolly Parton's breasts, in general humans like averages. Researchers confirmed that humans judge real faces by their differences or similarities from a norm. But they also found that the norm can change quickly: When researchers showed 164 people sets of 100 computer-generated faces representing a slow transition from male to female—and from Japanese to Caucasian—it turned out that the test subjects' idea of what constitute an "average" face shifted depending on the first face they saw. When they were flashed a super masculine face first, more faces on the spectrum impressed them, by contrast, as female. The masculine face had, in effect, set a standard. From then on, other faces had to be more masculine in order to rate as belonging to the gender. The study noted a similar shift using a scale of faces moving from surprise to disgust. The authors, who published their results in the journal Nature, conclude that in real life we also quickly change ore" perception of the midpoint—what's normal—depending on what we see. We may not be aware that our judgment has changed; we simply see differently, says Michael Webster, a psychologist at the University of Nevada in Reno and coauthor of the study. One implication is that individual and social attitudes toward what's acceptable, and what's beautiful, change over time. "If you look at plastic-surgery trends, in the 1950s and 1960s you saw little upturned noses," notes Harvard psychologist Nancy Etcoff, author of the book Survival of the Prettiest : The Science of Beauty. "Now the noses are broader and the lips are plumper. We're seeing images from around the globe, and it's changing our idea of the average. " So if you're unhappy with some aspect of your face, take comfort: beauty is a moving target.

单选题tRNA的反密码子能识别mRNA的密码子。反密码子的第一碱基能识别一个以上的密码子第三碱基(wobbling)者为 a．A； b．A和C； c．U和G； d．C。

单选题入噬菌体的裂解途径是由以下哪个蛋白基因控制? ____ 。

单选题原核mRNA的Shine-Dalgarno顺序通常是 a．多嘧啶序列； b．多嘌呤序列； c．嘌呤和嘧啶基本各半。

单选题某些个体在棕发中有一块白色或淡黄色的头发，这是哪一类突变造成的______。 A．性细胞突变 B．卵细胞突变 C．体细胞突变 D．配子突变

单选题E.coli F+adt+strs×ad-strr两种杂交，预期的菌株将在下列哪种培养基上被选择出来(ad是腺嘌呤的缩写)?( )

单选题自然选择学说不能解释( )。

单选题具有一对相对性状的亲本杂交后，子代中只表现一个亲本的性状，这种遗传现象称为______。 A.完全显性 B.不完全显性 C.共显性 D.超显性

单选题对性染色体的研究表明，人类性别决定是由( )控制的。

单选题转化、转导和性导的相同点在于______。 A.都需要噬菌体 B.都引起基因重组 C.都需要F因子 D.不引起重组

单选题Pedigree method or somatic cell hybridization can be used to map human chromosome genes. When the former is used to do chromosome mapping? ______. A．X chromosome linked genes are easier than somatic genes B．X chromosome linked genes are more difficult than somatic genes C．X chromosome linked genes are as easy as somatic genes D．All the above statements are incorrect because the data of pedigree method is unable to be used in chromosome mapping

单选题有一个杂交组合AaBbCc×AaBbCc，三个位点都是独立遗传并呈完全显性，那么在其后代中与亲代表现型完全相同的个体的概率是(假定未发生新的突变，也无更复杂的因子)______

单选题异序性是指：______。 A．T4噬菌体的环状排列基因次序模型 B．遗传重组时非姐妹染色单体之间形成的Holliday中间体交叉迁移造成的DNA双链异源性 C．由于倒位产生的融合基因表达的性状嵌合性 D．由于线粒体在细胞分裂中的无序性而造成的机体内各组织间遗传上的异质性