The XX-XY type of sex determination is present in which of the following organisms?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Both (1) and (2)
In the XY type of sex determination, the male has one X and one Y chromosome and the female has a pair of X chromosomes; both sexes have the same number of chromosomes. NCERT gives humans and Drosophila as the examples (Figure 4.12 a, b).
Option (1) Humans — Correct statement, but it is only one of the correct points, so on its own it is not the answer. In human beings the male is XY and the female XX, besides 22 pairs of autosomes.
Option (2) Drosophila — Correct statement, but it is only one of the correct points, so on its own it is not the answer. In Drosophila too, the male is XY and the female XX.
NCERT Extract:
Sex Determination – “… In a number of other insects and mammals including man, XY type of sex determination is seen where both male and female have same number of chromosomes. … Hence, the males have autosomes plus XY, while female have autosomes plus XX. In human beings and in Drosophila the males have one X and one Y chromosome, whereas females have a pair of X-chromosomes besides autosomes (Figure 4.12 a, b).”
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