Apea plant with yellow peas is crossed with a pea plant that has green peas. the offspring include both yellow-pea and green-pea plants. the original plant with yellow peas must, therefore, have what genotype?

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A pea plant with yellow peas is crossed with a pea plant with green peas. The offspring include both yellow-pea and green-pea plants in ratio 1:1. The original plant with yellow peas must therefore have what genotype?

a. YY

b. Yy

c. yy

d. It cannot be determined

The answer is Yy (heterozygous)

Explanation:

This cross involves a single gene coding for pea color in pea plants. Mendel performed this cross and discovered that the allele for yellow pea (Y) is dominant over the allele for green peas (y) i.e. allele Y will mask the phenotypic expression of allele y in a combined state. Hence, Y (yellow) is the dominant allele and y (green) is the recessive allele.

If a pea plant with the dominant phenotype (yellow pea) is crossed with a plant with recessive phenotype (green pea), alleles of the gene will separate into gametes and randomly fuse to form all yellow peas (Yy) if the yellow pea plant were homozygous dominant (YY).

In this case, the offsprings were both yellow and green in the ratio 1:1, this means that the original dominant plant (yellow phenotype) was heterozygous for the trait (Yy) since each allele (Y and y) will separate and combine with the alleles of the green pea plant that produces y and y only since it is homozygous recessive (yy). That is,

y. y

Y. Yy. Yy

y. yy. yy

Yy genotypes (2) are phenotypically yellow peas, while yy genotypes (2) are phenotypically green peas.

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