Question

Suppose there is a biochemical pathway for producing blue flower color that goes from white–>magenta–>blue. A dominant allele for gene 1 provides an enzyme that converts white–>magenta. A dominant allele for gene 2 provides an enzyme that converts magenta–>blue. A plant with magenta petals must have ______?

1) a dominant allele for gene 1
2) a dominant allele for gene 2
3) a recessive allele for gene 1
4) a recessive allele for gene 2

Answer 1

A plant with magenta petals in the described pathway indicates that it must have at least one dominant allele for gene 1, necessary for the white to magenta color change.

Step-by-step explanation:

If we consider a biochemical pathway for producing blue flower color that progresses from white to magenta to blue, and we know that a dominant allele for gene 1 catalyzes the conversion of white to magenta while a dominant allele for gene 2 catalyzes the conversion of magenta to blue, then a plant with magenta petals must have a dominant allele for gene 1. This is because the presence of magenta petals indicates that the first step of the pathway has occurred (white to magenta); however, the absence of blue petals suggests that the second step (magenta to blue) has not taken place. Since the second step requires a dominant allele for gene 2 and we only see magenta petals, gene 2 must not be present in its dominant form.

In the given biochemical pathway for flower color, the existence of magenta petals indicates the successful conversion from white to magenta, attributed to the presence of a dominant allele for gene 1. Since the conversion to blue does not take place, this implies that there is no dominant allele for gene 2 present. For the magenta color to manifest, it is essential that the organism at least be heterozygous for gene 1, possessing one dominant allele (e.g., Aa)