UNIT 4: Sex Determination and Sex Linkage
Exam Focus: Differentiate between chromosomal and environmental sex determination. Understand the mechanism of X-inactivation/Dosage Compensation (Barr Bodies). Be prepared to solve simple problems involving X-linked recessive inheritance like Colour Blindness or Haemophilia.
Table of Contents
1. Sex Determination
Sex determination is the biological system that determines the development of sexual characteristics in an organism.
Mechanisms of Sex Determination (Chromosomal)
The sex chromosomes (X and Y in humans) carry the genes that determine the sex.
| Type | Organism/Description | Female | Male |
|---|---|---|---|
| XX-XY Type | Humans, Mammals, Drosophila (though determined differently) | Homogametic (XX) | Heterogametic (XY) |
| ZZ-ZW Type | Birds, Reptiles, some Fishes | Heterogametic (ZW) | Homogametic (ZZ) |
| XX-X0 Type | Grasshoppers, Cockroaches | XX | X0 (one X chromosome) |