Question

Assume that humanlike creatures exist on Mars. As in the human population on Earth, there are two sexes and even sex-linked genes. The gene for eye color is an example of one such gene. It has two alleles. The purple allele is dominant to the yellow allele. A purple-eyed female alien mates with a purple-eyed male. All of the male offspring are purple-eyed, while half the female offspring are purple-eyed, and half are yellow-eyed. Which is the heterogametic sex? Draw out the two options of the Punnett squares in support of your explanation.

Answer 1

Female will be the heterogametic sex.

Purple coloured eye = ZpZp, ZpW, ZpZy

Yellow coloured eye = ZyZy, ZyW

The male can either be ZpZp or ZpZy

If male is ZpZp.

ZpZp × ZpW

Gametes	Zp
Zp	ZpZp purple male
Zy	ZpZy purple female

All progenies will be purple.

If male is ZpZy

ZpZy × ZpW

Gametes	Zp	W
Zp	ZpZp purple male	ZpW purple female
Zy	ZpZy purple male	ZyW yellow female

This is as per the question.

Male will be ZpZy.

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