Question

You are interested in analyzing the segregation of petal color in tulips over generations. You are tracking red and white petal colors, and lets assume that petal color results from a single-gene. You know from a trial cross that the F1 progeny from crossing a pure red tulip to a pure white tulip results in all red progeny. For the following questions, use the letters R and r to denote petal color genotype and make sure to clearly indicate the associated phenotypes.

Petal Color Questions
1. Based on the information given above, what do you know about which trait is dominant and which is recessive? Why?
a. If "R" is used to denote the genotype of the dominant allele, which petal color does "R" represent?
b. If "r" is used to denote the genotype of the recessive allele, which petal color does "r" represent?

Answer 1

1. R is dominant, and r is recessive. I know this information because the crossing of two pure red and white tulips means that the red tulip genotype is RR, and the white is rr. In other words, they are two h0m0zygous alleles. When we do a Punnet square, we can see that all the progeny is red since it is the trait that dominated over the white one.

a. R represents the red petal color.

b. r represents the white petal color.

Step-by-step explanation:

To determine which gene is the dominant and which one is the recessive, we have to look at the information that we have.

We know that the cross of a pure red tulip and a pure white tulip results in all red tulips. If we know that they are pure, they are hom0zygonious (RR and rr).

When we draw a Punnet square we can see that the offsprings will all have the genotype Rr and as we knew that offsprings were all red, we can deduce that the domiant trait is red (R), while the recessive one (white) is r. In other words, the dominat gene (red) will express itself while the recessive(white) won't. As a result, the tulips will be red.

║R║ R

r║Rr║Rr

r║Rr║Rr