Class 12 Biology Inheritance Variation SEX DETERMINATION


  • 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.

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