In pea plants, the allele for round seeds is dominant to the allele for wrinkled seeds. If a plant that is heterozygous for seed type is crossed with one that has only homzygous wrinkled seeds, what percent of their offspring would you expect to have wrinkled seeds?

50%

Explanation:

According to this question involving a gene coding for seed shape in pea plant, the allele for round seeds (R) is dominant to the allele for wrinkled seeds (r). This means that a heterozygous pea plant (Rr) will have a round seed shape.

If a plant that is heterozygous for seed type (Rr) is crossed with one that has only homzygous wrinkled seeds (rr), the following gametes will be produced by each parent plant:

Rr - R and r

rr - r and r

Using these gametes in a punnet square (see attached image), the following proportions of offsprings will be produced:

Rr, Rr, rr and rr

Rr = round seed offsprings

rr = wrinkled seed offsprings

Since 1 out of 2 offsprings has wrinkled seeds, 1/2 × 100 = 50% is the percentage of offsprings expected to have wrinkled seeds.