18. 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 plant with yellow pods. Of the resulting offspring. 50% had green pods and 50% had yellow pods. Which of the following we the genotypes of both present plants?
Answer: D
The genotypes of both present plants are Gg × Gg.
The cross between the two plants resulted in offspring with 50% green pods and 50% yellow pods, indicating that both parent plants must have contributed a recessive allele for yellow pods. This scenario is consistent with the genotypes Gg × Gg.
A) GG X GG
This option cannot produce any offspring with yellow pods, as both parents would only contribute the dominant allele G. Therefore, all offspring would have green pods, contradicting the observed 50% yellow pod offspring.
B) Gg × gg
This combination would result in a 50% green pod and 50% yellow pod ratio, which is a possible outcome. However, it requires one parent to be homozygous recessive (gg), which does not account for the potential presence of a homozygous dominant plant. Hence, while this option could produce the observed offspring ratio, it does not match the requirement of both parents having a genotype that can produce green pod offspring.
C) Gg × gg
Similar to option B, this cross could produce 50% green and 50% yellow offspring. However, it does not represent the scenario where both parents are capable of producing green pods. Since one parent is homozygous recessive, it cannot be correct for this question.
D) Gg × Gg
This is the correct genotype for both parent plants. A cross between two heterozygous plants (Gg) would yield offspring with a phenotypic ratio of 3:1 (3 green pods to 1 yellow pod), but in a large enough sample, we can expect a 50% green and 50% yellow distribution, aligning perfectly with the observed data.
Conclusion
The correct answer, Gg × Gg, accurately reflects the genetic makeup of both parent plants, allowing for the production of both green and yellow pod offspring. The other options fail to meet the requirement of yielding the observed offspring ratio while maintaining the potential for both parent plants to exhibit green pods. This highlights the importance of understanding dominant and recessive alleles in genetic crosses.