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哺乳动物的染色体构成,除少数例外,都是由动物种固有数目的二组常染色体和一对性染色体组成。而哺乳动物的性别被称为XX—XY型的机构所决定。雌性比雄性多一条X染色体,但其中一条在胚胎发生的极早期即被灭活,结果雌雄间的遗传差异只限于Y染色体。本来胚胎期未分化的性腺就有自动向卵巢发育的倾向,但向染色体构成中加入Y染色体时,则因Y的介入使未分化的性腺向睾丸发育。因此,由Y染色体决定性别。实际上在50年代末和60年代初期,已发现了Y染色体与睾丸发育之间的相互关系,而且
The chromosomes of mammals, with a few exceptions, consist of two sets of autosomal chromosomes and a pair of sex chromosomes, each of which is native to the animal species. The sex of the mammal is referred to as the XX-XY type of institution. The female had one more X chromosome than the male, but one of them was inactivated very early in the embryogenesis. As a result, the genetic difference between male and female was limited to the Y chromosome. Originally embryonic undifferentiated gonads have the tendency to develop automatically to the ovary, but to the chromosomal composition of the Y chromosome, due to the intervention of Y so that undifferentiated gonads to the testis development. Therefore, sex is determined by the Y chromosome. In fact, in the late 1950s and early 1960s, the correlation between the Y chromosome and testicular development has been found, and