生物工程专业英语.doc

生物工程专业英语 1 The Origin of Species Biologists Define a Species Modern biology generally define a species as group of actually or potenti ally interbreeding populationsthat is reproductively isolated from the such groups. Members ofa species can interbreed with each other,but they ca nnot breed anisms belonging to another species. One advantage of the standard ofreproductive isolation is that it is very precise. Notice, however, that it can only be applied anismsthat reproduce sexually. Asexual reproducers, including most prokaryotes, many plants, and some animals, must be classified into species on the basis of physical (biochemi cal or morphological) traits. 现代生物学大体将物种定义为实际上的一群或潜在的杂交群体, 即从这个群体隔离繁殖的后代。种族中个体可以互相交配,但种间不能。这种繁殖隔离的一个优势是很精确。但仅适用于性繁殖的生物。非性繁殖, 包括大多数原核生物, 许多植物, 某些动物, 需要通过自然特征进行归类。 Gene Exchange Two general types of mechanisms operate to block the exchange of genes between individuals of relatedgroups. The first general type is made up of prezygotic isolating mechanisms that prevent the formation ofzygotes. Prezygotic isolation falls into two categories: ecological and behavioral. In the first case, tworelated group may e adapted to slightly differe nt environments-perhaps varying soil types or foodsources. Over time, th ese ic differences e so great that essful cross-fertilization can nolonger take place. In behavioral isolation, related groups evolve di 生物工程专业英语 2 ffering behaviors such as specificmating rituals-that restrict the exchange of genes to members of the same group. 两种基因型机制阻碍了相关群体中个体的基因交换。第一种基因型由前合子机械隔离机制阻止合子的生成。前合子隔离分两类: 生态学的和行为学的。第一种情况, 两个相关群体可能分别适应稍微不同的环境, 如土壤类型或食物来源的变化。长时间, 这些遗传差异变得很大而很难异体受精。而行为学隔离, 相关的群组进化成不同的行为方式, 例如,结婚仪式,从而限制了同群成员基因交流。 Sometimes the differences that produce prezygotic isolation involve mech anical isolation. That is,mating is physically impossible between member s of different species because genitals of males andfemales are structurall y patible or because molecules on the surfaces of sperm and egg fai l