Question

In snapdragons, two genes control flower color, which can be red, pink, or white. Gene A encodes an enzyme that makes a precursor to red pigment, and gene R encodes the enzyme that makes the red pigment from the precursor. This makes Gene A epistatic to Gene R (if there is no precursor made, there can be no red pigment). Allele A (pigmented) is completely dominant to a (no pigment, white), and R isincompletely dominant to r. What would be the phenotypic ratio of a cross between an AaRr and an Aarr individual? If you choose this question, you may find it helpful to use the table tool in your answer window to create a punnett square.

Answer 1

The gene A encodes precursor where as gene R encodes red color from the precursor.

Here gene A is epistatic to gene gene R. It means when aa from of gene is present, then there is not found red color whether the other gene is in dominant form.

R is incompletely dominant over r allele.

RR encodes red color. Rr encodea pink color. rr encodes white.

Parents: AaRr × Aarr

Punnet square:

Gametes	Ar	ar
AR	AARr ( pink)	AaRr (pink)
Ar	AArr ( white)	Aarr ( white)
aR	AaRr (pink)	aaRr ( white)
ar	Aarr ( white)	aarr ( white)

​​Phenotypic ratio: White (5) : pink (3) : red (0)