He associated X body with sex determination. He discovered that, accessory chromosome forming unequal pair in one sex and equal in other sex and behave like sex factor is called as sex chromosome. The remaining chromosomes were called autosomes.
E.B. Wilson (1905) contributed valuable knowledge on the sex determination. Stevens (1905) showed that Drosophila fly has four pairs of chromosomes in somatic cells.
In male, one pair was peculiar as two members were of unequal sizes. One resembled the X chromosome of female. Wilson (1909) proposed Y chromosome for off chromosome in male.
Mechanism of sex determination:
It is the process by which a spore or egg (haploid/diploid) develops the properties of one or the other sex. The problem of sex determination has a very ancient history.
Following views were put forth by classical theorists and given more importance to external environment rather than reproductive cells.
1. Hippocrates and other theorists believed that sex of offspring depends on vigour of parent.
2. They thought that it depends on ripeness of ovum at the time of fertilization. If egg fertilized soon after ovulation females are developed and males are produced, if it remains in oviduct for some time before fertilization.
3. Galen and others claim that germ cell of right ovary produce male and left ovary produce female.
4. Schenk showed that control of mother’s diet produces sex at will i.e. high nourishment during pregnancy, produces females while less nutrition causes males.
5. Legends stated that phase of moon time of day during fertilization, wind direction and left or right testes also control the development of sex.
These speculations of different scientists are only of academic interest and are now replaced by genetic and scientific theories.