Question

In Alaskan malamute dogs, the allele for dwarfism (d) is recessive to the allele for normal-size dogs (D) and the allele for white coat colour (r) is recessive to the allele for brown coat colour (R). A breeder crosses two malamute dogs, both of normal-size and brown coat colour multiple times. During these multiple times, the following puppies were produced: Normal-size/brown coat colour: 18 Normal-size/ white coat colour: 6 dwarfism/brown coat colour : 6 dwarfism/white coat colour: 2 What genotype are the parent dogs?

Answer 1

DdRr

Step-by-step explanation:

The parents are heterozygous with the genotype DdRr.

Assuming the two genes are independently assorting. For standard, independently assorting genes, the phenotypic ratio for a dihybrid cross should be 9:3::3:1 with the domiant parental gene having the highest frequency, the recessive parental genes having the lowest frequency and the recombined genes having the intermediate frequencies.

DdRr x DdRr

Progeny

9 D_R_ normal size, brown coat

3 ddR_ dwarf, brown coat

3 D_rr normal size, white coat

1 ddrr dwarf, white coat.

The phenotypic frequency is 9:3:3:1.

Now let us look at phenotypic frequency of the outcome

18:6:6:2 is also equivalent to 9:3:3:1.

Hence, the parents are hetezygous with the genotype DdRr.