Question

Greg chose a yellow pea seed, the color of which is conferred by the Y allele. Y is completely dominant over the green y allele. He grew the yellow pea into a plant. In order to determine more about that plant's genotype, he performed a testcross of this plant with a green pea plant. He observed 92 green peas and 85 yellow peas among the testcross offspring. The conclusion he should make is:

-the genotype of the yellow pea plant was Yy

- the genotype of the green testcross parent was YY

- the genotype of the green testcross parent was Yy

- the genotype of the yellow pea plant was YY

Answer 1

In the question, nearly half offspring from the testcross of a yellow pea plant with a green pea plant show dominant phenotype and a half shows a recessive phenotype. This means that the plant is heterozygous for the trait. Please refer to the first point given in the explanation. Hence, the genotype of the yellow pea plant was Yy.

Explanation:

Two scenarios are possible from any test cross. They are summarized with the help of the following two points. Please read them. They shall help you in answering other questions of similar nature.

1. If half of the offspring from the testcross between a plant having an unknown genotype and a plant having recessive genotype show dominant phenotype and a half shows a recessive phenotype, the plant with unknown genotype is heterozygous for the trait. This means that the plant had one copy of the dominant allele and one copy of the recessive allele.
2. If all of the offspring from the testcross between a plant having an unknown genotype and a plant of recessive genotype show only the dominant phenotype, the plant with unknown genotype is homozygous for the trait. This means that the plant had two copies of the dominant allele.