Question

A mouse mating pair always produces an F1 with a phenotypic ratio of 2 earie : 1 WT. (earie is a shorting of the ears.) What are the genotypes of the parents (in the mating pair)?

Question 7 options:

	earie/earie X earie/earie.
	earie/earie X earie/+
	earie/earie X +/+
	earie/+ X earie/+
	earie/+ X +/+
	+/+ X +/+

Answer 1

Option D is correct.

Explanation:

2:1 monohybrid ratio represents a possible lethal homozygous condition for the mutant allele.

Here, earie can be a dominant allele. So, heterozygotes show mutant phenotype. For normal phenotype, both the alleles must be WT and homozygotes for the dominant allele are lethal.

So,

Parental cross: earie/+ X earie/+

Progeny genotypic ratio: 1:2:1

1. earie/earie (Lethal)

2. earie/+

1. +/+

Progeny phenotypic ratio = 2 (earie):1 (WT)