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众所周知,人类的核型为46条染色体,其中44条为常染色体(Autosome),2条为性染色体(Sex chromosome)。常染色体为男女共有的,而性染色体具 XX 者为女性,具XY 者为男性。人类在形成生殖细胞时,进行减数分裂所形成的含 X 和 Y 两种类型的精子应该是一样多的,那么两种精子分别与卵子结合的机会也应该是相等的,而出生的男女婴儿数量也应该一样多。因此,男女之间的比例(即性比)应该是1∶1,即性比平衡。由此而得知的所谓性比,是指雌性为100时的雄性数字。人类不同发育时期的性比如右表。
As we all know, human karyotype is 46 chromosomes, of which 44 are autosomes (Autosomes), two of sex chromosomes (Sex chromosomes). Autosomal shared by men and women, and sex chromosomes with XX are female, with XY were male. Human germ cells, the formation of meiosis to form the X and Y containing two types of sperm should be as much, then the two sperm and egg respectively, the opportunity should also be equal, and the birth of male and female babies The number should be as much. Therefore, the ratio between men and women (ie, sex ratio) should be 1: 1, that is, sexual balance. The so-called sex ratio thus obtained means the number of males at 100. Human sexual development at different times, such as the right table.