Sex Determination: Bridges had given the balance theory of Sex – determination.  Bridges

*Sex Determination in human being:

Human has 23 pairs of chromosomes out of which 22 pairs are autosomes and one pair is sex chromosomes. This one pair has 2 sex chromosomes XX in females and XY in males.

1. In Human beings and Drosophila female show homogamety and male shows heterogamety.
2. In birds like fowls and fishes, female shows heterogamety and male shows homogamety.

Female ZW and Male ZZ.

3. In Grasshopper family, male has only one X chromosome (Xo) and (XX) female has pair of X chromosomes.      
4. In Cockroach family, female has only one X chromosomes (Xo) and make has 2 (XX).

*Sex determination in honey bees:

In honeybee sex is determined by number of chromosomes.

1. Female has 32 chromosomes and formed by (egg + sperm) combination.
2. Mole has 16 chromosomes formed by parthenogenesis (without fertilization).