单选题细菌中各种mRNA所编码的蛋白质数目常有差异，据此有monocistronic，polycistronic和intereistronic之分。多数mRNA是 a．monocistronic mRNA； b．polycistronic mRNA； C．intercistronic mRNA。

单选题一个AB血型的男人与一个B血型的女人结婚，生了4个孩子，第一个是AB型，第二个为O型，第三个为AB型，第四个为A型。后来，由于夫妻不和，丈夫提出离婚，声称经血型家系分析，他不可能是所有孩子的父亲，他说的有道理吗?______

单选题以下群体中下遗传率最大的是______。 A．F1群体 B．F2混合群体 C．F3混合群体 D．F4群体混合

单选题家猫中有一位于常染色体上的基因杂合时，呈现无尾性状(只在骨盆上有痕迹)，而在纯合体时，又是致死的，那么当一无尾猫与另一无尾猫杂交时，子代表型为______

单选题在一个岛上，1999年的种群中，二倍体植物的等位基因Aa的频率为p(A)=0.90，q(a)=0.10，如假定2000年种群数仅为50，那么2000年失去等位基因a[p(A)=1]的概率是什么?

单选题One of the most important social developments that helped to make possible a shift in thinking about the r01e of public education was the effect of the baby boom of the 1950s and 1960s on the schools. In the 1920s, but especially in the Depression conditions of the 1930s, the United States experienced a declining birth rate—every thousand women aged fifteen to forty-four gave birth to about 118 live children in 1920, 89.2 in 1930, 75.8 in 1936, and 80 in 1940. With the growing prosperity brought on by the Second World War and the economic boom that followed it, young people married and established households earlier and began to raise larger families than had their predecessors during the Depression. Birth rates rose to 102 per thousand in 1946, 106.2 in 1950, and 118 in 1955. Although economics was probably the most important determinant, it is not the only explanation for the baby boom. The increased value placed on the idea of the family also helps to explain this rise in birth rates. The baby boomers began streaming into the first grade by the mid-1940s and became a flood by 1950. The public school system suddenly found itself overtaxed. While the number of schoolchildren rose because of wartime and postwar conditions, these same conditions made the schools even less prepared to cope with the flood. The wartime economy meant that few new schools were built between 1940 and 1945. Moreover, during the war and in the boom times that followed, large numbers of teachers left their profession for better-paying jobs elsewhere in the economy. Therefore, in the 1950s and 1960s, the baby boom hit an antiquated and inadequate school system. Consequently, the "custodial rhetoric" of the 1930s and early 1940s no longer made sense; that is, keeping youths aged sixteen and older out of the labor market by keeping them in school could no longer be a high priority for an institution unable to find space and staff to teach younger children aged five to sixteen. With the baby boom, the focus of educators and of laymen interested in education inevitably turned toward the lower grades and back to basic academic skills and discipline. The system no longer had much interest in offering nontraditional, new, and extra services to older youth.

单选题 在进行AB/ab′ab/ab测交时，如果有20％的卵母细胞在减数分裂时，a-b基因间形成了一个交叉节，测交后代中出现aaBb基因型的频率为。 A、10％ B、5％ C、20％ D、80％

单选题A commonplace in genetics is the relationship between recombination frequency and crossover value. Generally speaking, ______. A．recombination frequency may be directly obtained according to phenotypic ratios, but crossover value cannot be directly obtained according to phenotypic ratios B．crossover value may be replaced by recombination frequency or chiasm frequency you get from the observation under microscope when genetic distance is considerably short C．crossover value may be replaced by recombination frequency when genetic distance is as a medium value, not too long and not too short D．recombination frequency will be very different from crossover value when there is a third locus in between the two loci you analysed

单选题在减数分裂的前期Ⅰ的粗线期出现“十”字形图像，终变期形成“四体环”或“四体链”的个体应为______。 A．四体 B．同源四倍体 C．节段异源四倍体 D．相互易位杂合体

单选题对一生物减数分裂进行细胞学检查，发现后期Ⅰ出现染色体桥，表明该生物可能含有______。 A．臂间倒位染色体 B．相互易位染色体 C．臂内倒位染色体 D．顶端缺失染色体

单选题序列(IS)编码 ____ 。

单选题在20世纪30年代，对于生物进化过程中遗传和变异的研究，已经从( )。

单选题有人用菜豆作实验材料，用一个有色、大粒品系和另一白色、小粒品系杂交，得到的结果是：有色PP，45株，种子平均质量(0.307±0.05)kg；中间色Pp，80株，种子平均质量(0.283±0.03)kg；白色pp，41株，种子平均质量(0.264±0.05)kg。产生这些差异的可能原因是( )。

单选题以青霉素培养基作为选择培养基，用来筛选细菌的营养缺陷型，这一技术的原理是______。 A．青霉素可杀死敏感型细菌，只允许抗性细菌生存 B．青霉素有时可以补偿营养缺陷型，允许营养缺陷性细菌在基本培养基上生存 C．青霉素在营养缺陷型的菌落特征上，起明显的修饰作用，便于人们观察认识 D．青霉素可杀死繁殖的原养型细菌，只留下营养缺陷型

单选题亲缘关系相近的物种往往发生类似的突变，这叫做突变的______。 A．可逆性 B．重演性 C．平行性 D．有利性

单选题B∥B和Bb∥b果蝇复眼的大小不同，前者约有69个小眼，后者约有45个小眼，这是由于染色体______造成的。 A．重复的位置效应 B．重复的剂量效应 C．缺失 D．臂内倒位

单选题假定A—ａ，B—b，C—c三刘甚因彼此独立遗传，则AABbCc和AaBbCc杂交所得到的后代中出现基因型为AABBcc个体的概率是