The ZW-ZZ type of sex determination is found in which of the following organisms?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Birds
In the XO and XY types of sex determination the male makes two kinds of gametes (male heterogamety). In birds it is the female that makes two kinds of gametes (female heterogamety). To mark the difference, the sex chromosomes of birds are called Z and W: the female is ZW and the male ZZ.
Option (1) Drosophila — Incorrect. Drosophila has the XY type: the male has one X and one Y chromosome and the female has a pair of X chromosomes.
Option (2) Human beings — Incorrect. Human beings also have the XY type, with XY males and XX females.
Option (3) Grasshopper — Incorrect. The grasshopper has the XO type: the male has only one X chromosome and the female has a pair of X chromosomes.
Option (4) Birds — Correct. In many birds the female has two dissimilar sex chromosomes, Z and W, while the male has a pair of Z chromosomes.
NCERT Extract:
Sex Determination – “… But two different types of gametes in terms of the sex chromosomes, are produced by females, i.e., female heterogamety. 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.”
Figure 4.12 Determination of sex by chromosomal differences: (a,b) Both in humans and in Drosophila, the female has a pair of XX chromosomes (homogametic) and the male XY (heterogametic) composition; (c) In many birds, female has a pair of dissimilar chromosomes ZW and male two similar ZZ chromosomes