Dihybrid Cross

Tutorial to help answer the question

Problem 1: Predicting combinations of alleles in gametes of plants heterozygous for two traits.

A pea plant is heterozygous for both seed shape and seed color. S is the allele for the dominant, spherical shape characteristic; s is the allele for the recessive, dented shape characteristic. Y is the allele for the dominant, yellow color characteristic; y is the allele for the recessive, green color characteristic. What will be the distribution of these two alleles in this plant's gametes?

Tutorial

Assortment of Ss alleles

The gametes from the SsYy parent will receive one of the two alleles Ss.

Half will receive the dominant S allele, and half the recessive s allele.

Assortment of Yy alleles

The gametes from the SsYy parent will also receive one of the two alleles Yy.

Half will receive the dominant Y allele, and half the recessive y allele.

Possible combinations of alleles in gametes of plants heterozygous for two traits.

Since alleles of different traits segregate independently during gamete formation, there is the same probability that the Y (or y) allele will segregate with the S allele as with the s allele.

Thus all four combinations of gametes (SY, Sy, sY, sy) are equally probable.

The Biology Project
University of Arizona
Friday, August 9, 1996
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