As indicated in the diagram enzyme a catalyses the

Question

The following information applies to the next two questions.

In carrots, the normal colour of the root is orange. The production of the orange pigment can be illustrated by the pathway shown below:

As indicated in the diagram, Enzyme A catalyses the conversion of the yellow compound, Precursor A, to another yellow compound, Precursor B. Enzyme B catalyses the conversion of Precursor B to the final orange compound.

Question

Two true breeding variant strains have been observed, both of which produce yellow roots. One of the variants contains a mutation in the gene encoding Enzyme A and the other variant carries a mutation in the gene encoding Enzyme B. When these true breeding strains are crossed together the resulting F₁ progeny all possess orange roots.

Given this information, is the yellow phenotype of the two variants recessive or dominant to the wild-type orange phenotype?

The F₁ were allowed to self cross. Draw a Punnet Square and determine what phenotypic ratio will be observed in the F₂.