In pea plants, green pod color (G) is dominant to yellow pod color (g). A cross was done between a plant with green pods and a plant with yellow pods. Of the resulting offspring, 50% had green pods and 50% had yellow pods. Which of the following were the genotypes of both parent plants?
A.
gg x gg
B.
Gg x gg
C.
Gg X Gg
D.
GG x gg
The Correct answer and Explanation is:
The correct answer is B. Gg x gg.
Explanation:
In this genetic cross involving pea plants, we need to understand the inheritance of pod color, where green pod color (G) is dominant over yellow pod color (g). To analyze the scenario, let’s break down the information provided:
- Parental Plants: One plant has green pods, while the other has yellow pods. Since yellow pod color is recessive, the yellow pod plant must have the genotype gg (homozygous recessive).
- Offspring Ratios: The offspring of the cross show a 50% green pod color and 50% yellow pod color distribution. This ratio indicates that the green pod parent must carry one allele for yellow pod color (g), making its genotype heterozygous Gg.
Analysis of Other Options:
- Option A: gg x gg would result in all offspring being yellow (gg) since both parents are homozygous recessive.
- Option C: Gg x Gg would produce offspring in a ratio of 3:1 (75% green to 25% yellow) because it would yield GG, Gg, Gg, and gg genotypes.
- Option D: GG x gg would produce all green pods (Gg), as all offspring would receive a G allele from the GG parent and a g allele from the gg parent.
Punnett Square:
To confirm, let’s construct a simple Punnett square for the cross Gg x gg:
| g | g | |
|---|---|---|
| G | Gg | Gg |
| g | gg | gg |
- From this square, we can see that there are two Gg (green pods) and two gg (yellow pods). This leads to a ratio of 2 green (50%) to 2 yellow (50%) pods, consistent with the offspring observed.
Thus, the only viable explanation for the 50% green and 50% yellow pod ratio in the offspring is the cross of a heterozygous green pod plant (Gg) with a homozygous yellow pod plant (gg).