单选题大肠杆菌的克隆载体中，常规使用的质粒载体可以克隆的最大DNA片段是( )。 A．300～400bp B．25kb C．15kb D．40kb

单选题产气荚膜梭菌侵入宿主是通过( )途径。 A．消化道 B．呼吸道 C．皮肤创口 D．泌尿生殖道

单选题在工业生产中为提高土霉素产量，培养基中可采用的混合氮源是( )。 A．蛋白胨/酵母浸膏 B．黄豆饼粉/花生饼粉 C．玉米浆/黄豆饼粉 D．玉米浆/(NH4)2SO4

单选题______是合成核酸的主体物。( ) A．5-D核糖 B．5-D木酮糖 C．5-D甘油醛

单选题在下列原核生物分类中，属古细菌类的细菌是：( ) A．大肠埃希氏菌B．支原体 C．放线菌 D．产甲烷细菌

单选题用紫外线诱变处理，获得了产糖化酶活力提高的菌株，这种现象说明( ) A．突变是诱变产生的 B．突变结果与原因不相对应 C．是移码突变的结果 D．是碱基转换的结果

单选题关于登革热的叙述不正确的是

单选题白喉棒杆菌被β噬菌体溶源化后，成为产毒株，此即( )。 A．转化 B．转导 C．转染 D．溶源转变

单选题病人鼻咽部分离出一株白喉杆菌，要确诊为白喉还需要

单选题真核生物基因克隆和表达时，目的基因的获得不能采用的方式是( )。 A．DNA文库筛选 B．cDNA文库筛选 C．PCR体外扩增 D．DNA的合成

单选题需要载体但不能进行逆浓度运输的是( )。 A．主动运输 B．扩散 C．促进扩散 D．基团转位

单选题和豆科植物共生固氮的微生物是( )。 A．假单胞菌 B．根瘤菌 C．蓝细菌 D．自生固氮菌

单选题 依据cDNA建立的图谱应该称为（ ） A、遗传图谱 B、序列图谱 C、转录图谱 D、物理图谱

单选题如果想知道成年人是否是XXY型，最简单的方法是______。

单选题a和b的重组值为20%，在AB/ab自交后代中，ab表型的比例为：( )。

单选题 若一个物种的染色体组成是2n=AABB=a1a1a2a2a3a3a4a4b1b1b2b3b3b4b4，则该物种是（ ）。 A、同源四倍体 B、异源四倍体 C、同源异源四倍体 D、异源八倍体

单选题用二项展开式描述多对相互独立基因经自由组合，产生后代的基因型时，二项式的指数n代表( )。

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 关于重复力的叙述，错误的是（ ）。　　 A、重复力是衡量同一个体某一数量性状多次度量值之间的相关程度的指标 B、重复力是一个组内相关系数 C、重复力反映了一个性状受到遗传效应和持久环境效应影响的大小 D、重复力越高说明需要度量的次数越多

单选题一外生殖器异常患者，染色质检查发现有X小体2个，Y小体1个，其核型可能为______。