Question

You are breeding a species of mountain lion (2n); you cross a true breeding male that has straight yellow fur with a true breeding female that has curly red fur.   The offspring have curly orange fur; based on your results, what is the mode of interaction between the alleles?

a. You can’t tell mode of interaction because you don’t know which offspring is a heterozygote

b. Curly fur is dominant to straight fur and yellow and red fur colour show incomplete dominance

c. Fur shape (curly/straight) is determined by simple dominant/recessive relationship between the alleles while the environment influences fur colour.

d. Curly fur is dominant to straight fur and yellow fur colour is co-dominant to red

After breeding your mountain lions you also studied the ears of the offspring. The female parent had straight ears and the male parent had folded ears, amongst the offspring  - 100% of the female offspring had folded ears and 100% of the male offspring had straight ears.

What is the mode of inheritance for straight ears?

a. X-linked recessive

b. Sex-limited

c. Y-linked

d. X-linked dominant

Answer 1

As the offspring have curly orange fur, the mode of interaction between the alleles is:

b. Curly fur is dominant to straight fur and yellow and red fur colour show incomplete dominance

This is because the true breeding female has curly fur (let us consider FF) and the true breeding male has straight fur (let us consider ff), the heterozygous offspring (Ff) will have curly fur.

The true breeding male has yellow fur and the true breeding female has red fur; and the offspring has orange fur. This indicates incomplete dominance as the dominant allele(red) does not completely mask the effect of recessive allele(yellow) and the resulting phenotype is a blend (orange) of both phenotypes.

Also environment doesn't determine the phenotype of offspring and co dominant expression shows expression of both alleles from parent equally

The mode of inheritance for straight ears is:

a. X-linked recessive

Let us indicate the genotype of female parent with straight ears as XsXs and the male parent with folded ears as XY.

Genotype of parent XsXs x XY

↓

Genotype of offsprings XsX XsY

So 100% of the female offspring have folded ears and 100% of the male offspring have straight ears, as the X and Y allele is dominant to the Xs allele.