Sex Determination in Human Beings

The mechanism of sex determination has always been a puzzle before the geneticists. The initial clue about the genetic/chromosomal mechanism of sex determination can be traced back to some of the experiments carried out in insects.

In fact, the cytological observations made in a number of insects led to the development of the concept of genetic/chromosomal basis of sex-determination. Henking (1891) could trace a specific nuclear structure all through spermatogenesis in a few insects, and it was also observed by him that 50 percent of the sperm received this structure after spermatogenesis, whereas the other 50 percent sperm did not receive it. Henking gave a name to this structure as the ‘X body’ but he could not explain its significance.

• Finalization of sex at the time of zygote formation is called sex determination.

• Two types of chromosomes are present in individuals – sex chromosomes (which determine the sex of individual) and autosomes.

SEX DETERMINATION IN HUMANS

• Humans show XY type of sex determination mechanism.

• Out of 23 pair of chromosomes, 22 are autosomes (same in both males and females).

• Females have a pair of X chromosomes.

• Males have an X and a Y chromosome.

• During spermatogenesis Males produce two types of gametes with equal probability - sperm carrying either X or Y chromosome.

• During oogenesis females produce only one type of gamete having X chromosome.

• An ovum fertilized by the sperm carrying X-chromosome develops into a female (XX) and an ovum fertilized by the sperm carrying Y-chromosome develops into a male(XY).