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 per cent of the sperm received this structure after spermatogenesis, whereas the other 50 per cent sperm did not receive it.

✅Henking gave a name to this structure as the X body but he could not explain its significance.

✅Further investigations by other scientists led to the conclusion that the ‘X body’ of Henking was in fact a chromosome and that is why it was given the name X-chromosome.

✅It was also observed that in a large number of insects the mechanism of sex determination is of the XO type, i.e., all eggs bear an additional X-chromosome besides the other chromosomes (autosomes). On the other hand, some of the sperms bear the X-chromosome whereas some do not.

✅Eggs fertilized by sperm having an X-chromosome become females and, those fertilized by sperms that do not have an X-chromosome become males.

✅Due to the involvement of the X-chromosome in the determination of sex, it was designated to be the sex chromosome, and the rest of the chromosomes were named as autosomes.

✅Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.

✅These observations led to the investigation of a number of species to understand the mechanism of sex determination.

✅In a number of other insects and mammals including man, XY type of sex determination is seen where both male and female have same number of chromosomes