In pea plants, round peas (R) are dominant to wrinkled peas (r). You do a test cross between a pea plant with wrinkled peas (genotype rr) and a plant of unknown genotype that has round peas. You end up with three plants, all which have round peas. From this data, can you tell if the parent plant is homozygous dominant or heterozygous?

Question

Caitlin Brown

Biology

1 September, 19:02

In pea plants, round peas (R) are dominant to wrinkled peas (r). You do a test cross between a pea plant with wrinkled peas (genotype rr) and a plant of unknown genotype that has round peas. You end up with three plants, all which have round peas. From this data, can you tell if the parent plant is homozygous dominant or heterozygous?

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Answers (1)

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Joseph Hunter · Answer 1

The parent plant is a heterozygous.

Explanation:

If we have a recessive phenotype, the only way that the result ends up with a 75% of a dominant phenotype is doing a test cross with a dominant phenotype that have a heterozygous genotype. When both genotype are homozygous, the result ends up with a 100% of a dominant phenotype because if we do a test cross between them, the result is a combination of a dominant allele and a recessive one, therefore every time we have this combination (a heterozygous genotype) the phenotype that is showed is the dominant one, even tough there is a recessive allele.