Question

Is the sperm or the egg is responsible for the sex of the chicks?

Answer 1

Hint: Birds have a ZW system of sex determination. The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), and in some reptiles.

Complete answer:
Only the egg is responsible for the sex of the chicks. If the egg containing Z chromosome combines with sperm then it will result in the male formation and if the egg-containing W chromosome combines with the sperm, it will result in female formation.

Additional Information: In birds, the sex of the embryo is determined by the egg, not the sperm (as it is in humans). Avian sex differentiation is not determined by XY chromosomes like it is in humans and most mammals (or even the XO system used by some insects). In those systems, the sex is determined by the sperm, by what the male contributes to the offspring. By contrast, birds have a ZW system of sex determination (shared with butterflies, moths, fish and reptiles). In that system, sex is determined by the female within her ova, and the sex of offspring is not affected at all by the sperm which the male contributes. Some people think it is this difference which makes parthenogenesis possible for birds. Parthenogenesis occurs when unfertilized eggs see embryonic development.

Note: A sex-determination system determines the event of sexual characteristics in an organism. Most organisms that make their offspring by heterogametic fusion have two sexes. Occasionally, they are hermaphrodites in place of one or both sexes. The sex of the offspring will be the sex of either one of the parent. Few of the examples are given below.

Organism	Male sex chromosome(father)	Female sex chromosome(mother)	Sex determined by(father/Mother)
Human beings	XY	XX	Father
Birds	ZZ	ZW	Mother
Grasshoppers, crickets, and some other insects	XO	XX	Father