Identify the correct mechanism of sex determination in insects.

The correct answer is Option (1) → XO type

Note: The given answer is as per the official NTA Answer Key. However, the question can have more than one correct answer, i.e. both Option (1) and Option (2), because NCERT says that the XY type of sex determination is also seen in a number of insects, as explained below.

Sex is decided by the sex chromosomes. In insects more than one pattern is found.

(1) XO type — Correct. In a large number of insects (the grasshopper is an example) all eggs carry an extra X chromosome. Some sperms carry an X and some do not. An egg fertilised by a sperm with X gives a female (XX). An egg fertilised by a sperm without X gives a male (XO). This is the answer given by NTA.

(2) XY type — Also correct as per NCERT. In a number of other insects, and in mammals including man, the XY type is seen. Drosophila is an insect with XX females and XY males.

(3) ZW type — Incorrect. This is found in birds. The female has the two unlike chromosomes ZW and the male has ZZ.

(4) XX type — Incorrect. This is not a mechanism. XX is only the make-up of the female in the XY and XO types.

NCERT Extract:
Sex Determination – …