Question

Clicker question 5 You are studying two linked genes that influence hair type and eye color in mice. Straight hair (H) is dominant over curly (h), and brown eyes (E) are dominant over blue (e). You get the following numbers of offspring from a dihybrid testcross: Straight hair, blue eyes 101 Curly hair, brown eyes 104 Straight hair, brown eyes 15 Curly hair, blue eyes 17 Which of the following drawings shows the allele arrangement in the dihybrid? A. B. C. D. h e HE H e He h e h e h E H

Answer 1

In case of linkage, parental combinations have high frequency and recombinations have low frequency in the offsprings.  

There are two types of linkage :

Cis - both linked genes are dominant or recessive

Trans - one of the linked gene is dominant and other is recessive.

Here in the question, their is a cross between a dihybrid ( HhEe) and recessive genotype (hhee). The offsprings number is given in the question and we can conclude that the combination with high frequency are straight hair and blue eyes(101) and curly hair and brown eyes (104).

We can find allele arrangement by finding the genotype of the offsprings with parental combinations. We know that there would be 4 types of gametes from a dihybrid and one type of gamete from recessive one. So , the offsprings would always have atleast one recessive allele for both the genes from the recessive individual.  

So the genotypes of individuals with parental combinations are:

Hhee - from gametes with allele he(from recessive)and He( from dihybrid)

hhEe - from gametes with allele he(from recessive) and hE (from dihybrid)

Hence, the linked genes are hE and hE. So option C is correct. This is a trans linkage.

HhEe dihybrid parent hhee recessive gametes He - Hh Ee Hhee hh Ee hhee 15 101 (parental combinat 104 (parental combination) 17 -