单选题果蝇多是有翅的，但后来产生了残翅的类型，这些类型的个体在森林中难以生存，但在海岛上去生活得很好，这说明( )。

单选题姊妹染色单体是在细胞周期的______期形成的。 A.前期 B.中期 C.末期 D.间期

单选题对玉米F2籽粒颜色进行统计，发现一个样本的252粒总数中有1粒与祖代相同，另一个样本的507粒总数中有2粒与祖代相同。控制玉米籽粒颜色有______对。 A．1对 B．2对 C．3对 D．4对

单选题豌豆中，高茎(T)对矮茎(t)为显性，黄子叶(Y)对绿子叶(y)为显性，假定这两个位点的遗传符合孟德尔第二定律，若把真实遗传的高茎黄子叶个体与矮茎绿子叶个体进行杂交，F 2 代中矮茎黄子叶的概率是______

单选题下面是关于红色脉孢霉(Neurospora crassa)遗传分析的陈述，请选择最佳选项。______ A．由于红色脉孢霉的子囊狭窄，减数分裂后的4个同源染色体在子囊中顺序排列 B．作为细菌遗传分析的模式物种，红色脉孢霉可以利用着丝粒作图法进行基因定位 C．在红色脉孢霉中，减数分裂第二次分裂(MⅡ)的比例可用于计算某基因位点与着丝粒的重组率 D．由于红色脉孢霉的子囊狭窄，减数分裂后的4个染色单体在子囊中顺序排列

单选题转座作用前后DNA的含量变化是： ____ 。

单选题The inheritance pattern of dimple is dominant. A man with dimples who was married by a woman without dimples gave birth to 8 children, and interestingly, all the eight children have dimples in their faces. The most possible genotype of this man is______． A．Aa B．AA C．aa D．unable to be inferred

单选题下列细胞器中，拥有遗传物质DNA或RNA，且具有内外两层膜结构的是

单选题细菌中，同源重组发生在一些热点周围，这和 ____ 在chi位点上的单链内切酶活性有关。

单选题George Williams, one of Scottsdale's last remaining cowboys, has been raising horses and cattle on his 120 acres for 20 years. The cattle go to the slaughterhouse, the horses to rodeos. But Mr. Williams is stomping mad. His problems began last year when dishonest neighbours started to steal his cattle. Then other neighbours, most of them newcomers, took offence at his horses roaming on their properties. Such grumbles are common in Arizona. The most recent Department of Agriculture census shows that 1 213 of Arizona's 8 507 farms closed down between 1997 and 2002. Many cattlemen are moving out to remoter parts of the state. Doc Lane is an executive at the Arizona Cattlemen's Association, a trade group. He says Arizona's larger ranch owners are making decent profits from selling. It is the smaller players who are the victims of rising land values, higher mortgages and stiffer city council rules. What happens all too often is that people move in next to a farm because they think the land pretty. But soon they start complaining to the council. In Mr. Williams's case it was the horses that annoyed them. Other newcomers don't like the noise, the pesticides and the smell of manure. Locals worry about the precious, dwindling cowboy culture. Arizona's tourism boards like to promote a steady interest in all things about cowboy and western. Last year more British and German tourists came than usual, and many of them were looking precisely for that. Arizona's Dude Ranch Association fills its $ 350-a-night luxury ranches most of the year; roughly a third of the guests are European. Many of the ranchers themselves see all this tourism as a cheeky attempt to commercialise a real and vanishing culture. In Prescott, estate agents promote "American Ranch-style" homes with posters of horse riders. On the other side of the street is Whiskey Row, a famous strip of historic cowboy bars. But in Matt's Saloon on Saturday night, real cattlemen could not be found. Farm folk like Mr. Knox and Mr. Williams are weighing up their options. Many will migrate to remoter places where land is cheaper and not crowded with city people. Younger ones take on side-jobs as contractors and are cattle-hands part-time. Older cowboys aren't sure what to do.

单选题具有一对杂合基因的个体连续自交______代，才能使约97%的个体纯合。 A．3 B．5 C．6 D．7

单选题整合到细菌染色体上的噬菌体是______。 A．烈性噬菌体 B．原噬菌体 C．假噬菌体 D．转导颗粒

单选题由n与n+1配子结合产生的后代是______。 A．单体、亚倍体 B．三体、亚倍体 C．单体、超倍体 D．三体、超倍体

单选题关于染色体复制和细胞减数分裂的正确说法是______。 A．染色体复制1次细胞分裂2次 B．染色体复制2次细胞分裂1次 C．染色体复制1次细胞分裂1次 D．染色体复制2次细胞分裂2次