- Different organisms have different types of sex determination.
- Cytological observations in insects led to the development of concept of genetic or chromosomal basis of sex-determination.
- In 1891, Henking traced a specific nuclear structure all through spermatogenesis in few insects.
- He observed specific nuclear structure is located on 50 per cent of sperms only. The discovered X-body but was unable to explain its significance.
- In insects, XO type of sex determination is present. All the eggs have an additional X-chromosome besides the autosomes. Some sperms bear X-chromosome where as some do not.
- Eggs fertilized by sperm having having X-chromosome become females and those fertilized by sperms that do not have an X-chromosome becomes males.
- For example: grasshopper (males have only one X-chromosome besides autosomes and females have a pair of X-chromosomes)
Pic shows Sex determination in Insects.