Question

Assertion: XX-YY type of sex determination mechanism is an example of female heterogamety and is found in Drosophila.
Reason: Male heterogamety is seen in moths where males produce two different types of gamete.
A. Both assertion and reason are correct and the reason is the correct explanation for the assertion.
B. Both assertion and reason are correct but the reason is not the correct explanation for the assertion.
C. The assertion is correct but the reason is incorrect.
D. Both assertion and reason are incorrect.

Answer 1

To get the correct answer, one should know the chromosome gametic system present in drosophila and moths. For example, humans follow a heterogamety chromosome system where the presence of the Y chromosome decides the sex of the progeny.

Complete answer:
Sex determination is a process that decides what the progeny will be based on which gametes are fusing to form a zygote. Sexual differentiation is triggered by the main gene present on the sex locus with the other genes which has dominant effects.
In fruit flies or drosophila females have XX sex chromosomes and males have XY sex chromosomes. Which do not support the assertion and it is wrong.
In Lepidoptera such as moths and butterflies, females have a heterogametic sex chromosome system that is WZ and male moths have ZZ homogametic chromosome system which proves the given reason wrong.

So, the correct answer is D which is “both assertion and reason are incorrect”.

Additional information:
In some of the species, the external environment such as temperature plays a major role in sex determination. This process is not fully studied yet. In some species of plants and fish, they do not have fixed sex. They undergo a life cycle and change the sex based on genetic cues depending upon the lifestyle they follow. This also could be due to environmental factors such as seasons and temperature.

Note:
In Drosophila, the X chromosome determines sex, unlike humans where the Y chromosome decides the sex. In drosophila when progeny has only X chromosome and absence of the Y chromosome, the progeny will be sterile males.