Question

In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds?

a) None
b) 1/4
c) 1/2
d) 3/4

Answer 1

In a genetic cross of two heterozygous pea plants (Ss), the fraction of offspring with spherical seeds is 3/4, as determined by a Punnett square analysis demonstrating that three out of four possible genotypes will exhibit the dominant spherical seed phenotype. Option D is correct.

Step-by-step explanation:

The question is regarding inheritance patterns in pea plants, specifically the dominance of spherical seeds over dented seeds. To determine the fraction of offspring having spherical seeds, when heterozygous plants are crossed, we employ a Punnett square.

Each heterozygous plant can produce two types of gametes, S (spherical) and s (dented). When we cross Ss × Ss, the Punnett square yields the following genotypes: SS, Ss, Ss, and ss. As a result, seeing that S (spherical) is dominant over s (dented), three out of four possible genotypes (SS, Ss, and Ss) will exhibit the spherical seed phenotype. So, the fraction of offspring with spherical seeds is 3/4.

In pea plants, round peas (R) are dominant to wrinkled peas (r). When two plants that are heterozygous for the seed shape trait (Rr) are crossed, the offspring will have a 3/4 chance of having spherical seeds. This is because the dominant allele for seed shape (R) will be present in three out of the four possible genotypes in the Punnett square analysis: RR, Rr, and Rr.