Question

How is the sex-determination mechanism different in the birds? Is the sperm or the egg responsible for the sex of the chicks?

Answer 1

Sex determination in birds:
Female bird :

• In birds, females have two different sex chromosomes designated as $Z$ and $W$ chromosomes beside autosomes.
• Hence, females show heterogamety, that is, two types of gametes will be formed by the female.

Male bird:

• In birds, males are homogametic. They have a pair of $Z-$ chromosomes (sex chromosomes) besides the autosomes.

Since the gametes produced by the female birds will have different sex chromosomes, so, in the case of birds, female determines the sex of the offspring.

Sex determination in humans :
Female human :

• In human, females have a pair of same sex chromosomes ($X$ chromosomes) beside autosomes.
• Hence, females show homogametic, that is,the gametes formed by human females will be of the same type.

Male human :

• In humans, males are heterogametic. They have two different sex chromosomes designated as $X$ and $Y$ chromosomes besides the autosomes.

Since the gamete produced by human males will have different sex chromosomes,so, in the case of human, male determines the sex of the offspring.

Difference in sex determination in birds and humans :

Criteria	Sex determination in Birds	Sex determination in Humans
Set of chromosomes in females	Autosomes $+ZW$ Female heterogametic	Autosomes $+XX$ Female homogametic
Set of chromosomes in males	Autosomes $+ZZ$ Male homogametic	Autosomes $+XY$ Male heterogametic

Sex determination in chicks :
Chicks are birds. Sex is determined in chicks in the same way it is determined in other birds.

• Female shows heterogamety, by having two different sex chromosomes designated as $Z$ and $W$ beside autosomes.
• The males are homogametic, having only a pair of $Z-$ chromosomes besides the autosomes.
• Since the gametes produced by the chicks will have different sex chromosomes, so, in the case of chicks, female determines the sex of the offspring.

Diagrammatic representation of sex determination in birds :