in pea plants, green pod color (6) is dominant to yellow pod color ( 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.
Ggx Gg
B.
GG x gg
C.
Gg x gg
D.
gg x gg
The Correct answer and Explanation is:
To solve this problem, we first need to understand the genetics of pod color in pea plants. The green pod color (G) is dominant to the yellow pod color (g). Therefore, any plant with at least one dominant allele (G) will exhibit green pods, while only plants with two recessive alleles (gg) will have yellow pods.
The key information provided is that a cross was made between a plant with green pods and a plant with yellow pods, resulting in offspring where 50% had green pods and 50% had yellow pods. This ratio suggests that the green pod parent must have contributed a recessive allele (g) to half of the offspring, allowing for some to exhibit the yellow pod phenotype.
Let’s analyze the options:
A. Gg x Gg: This would yield offspring with a 75% green (GG and Gg) and 25% yellow (gg) ratio, which does not match our 50-50 ratio.
B. GG x gg: This cross would produce 100% green offspring (all Gg), as GG can only contribute the dominant allele. This also does not match the observed offspring.
C. Gg x gg: In this cross, the Gg parent can contribute either G (dominant) or g (recessive), while the gg parent can only contribute g. The possible offspring would be 50% Gg (green pods) and 50% gg (yellow pods), which matches the given results.
D. gg x gg: This cross would result in 100% yellow offspring (all gg), which also does not fit our observed results.
Given this analysis, the correct answer is C. Gg x gg.
Explanation
In a monohybrid cross, where one trait is being examined, the genotypes of the parents determine the phenotypic ratio of the offspring. In our case, the green pod color (G) is dominant, and the yellow pod color (g) is recessive. When a heterozygous green pod plant (Gg) is crossed with a homozygous recessive yellow pod plant (gg), the offspring inherit one allele from each parent.
The possible combinations from the Gg x gg cross are:
- Gg (green pods)
- gg (yellow pods)
This results in a 50% ratio of green to yellow pods in the offspring, which perfectly aligns with the scenario described in the question. Therefore, the genotypes of the parent plants must be Gg for the green pod plant and gg for the yellow pod plant.