In some organisms, male has ZZ chromosomes and female has ZW chromosomes. This type of sex-determination is found in:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Hen
In ZZ–ZW sex determination the female is heterogametic (ZW, two kinds of eggs) and the male is homogametic (ZZ). So the egg decides the sex of the chick.
Option (1) Drosophila — Incorrect. In Drosophila the male is XY and the female XX.
Option (2) Hen — Correct. In birds, the female is heterogametic with Z and W chromosomes, while the male is ZZ. The hen is a bird, so it shows this ZW-ZZ type of sex determination.
Option (3) Cockroach — Incorrect. Cockroaches (like grasshoppers) have the XO type: the male has only one X.
Option (4) Snail — Incorrect. Most snails are hermaphrodites; NCERT does not give them a ZW system.
NCERT Extract:
Sex Determination – “… In order to have a distinction with the mechanism of sex determination described earlier, the two different sex chromosomes of a female bird has been designated to be the Z and W chromosomes. In these organisms the females have one Z and one W chromosome, whereas males have a pair of Z-chromosomes besides the autosomes.”