Sex Determination Mechanism – Class 12 | Chapter – 5 | Biology Short Notes Series PDF
Sex Determination Mechanism: A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes.
Sex Determination Mechanism
- Finalization of sex at the time of zygote formation is called sex determination.
- Two types of chromosomes are present in individuals – sex chromosomes (which determine the sex of individuals) and autosomes.
1. XX-XY TYPE
Seen in many insects and mammals including humans, Drosophila melanogaster. Males have X and Y chromosomes along with autosomes [A] and females have a pair of X chromosomes.
2. XX-XO TYPE
Seen in grasshopper. Males have only one X chromosomes besides autosomes and females have a pair of X chromosomes.
3. ZZ-ZW TYPE
Seen in birds, fowl and fishes. Females have one Z and one W chromosomes whereas males have a pair of Z chromosomes.
4. XX-XY TYPE
Seen in cockroaches. Females have only one Z chromosomes besides autosomes and males have a pair of Z chromosomes.
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