In pea plants, the allele for smooth pods (S) is dominant over the allele for pinched pods (s). Construct a Punnett square that shows a cross between an Ss plant and an Ss plant. Predict what percent of the offspring are likely to have smooth pods.
*
4 points
50%
100%
75%
25%
To construct a Punnett square for a cross between an Ss plant and an Ss plant, we first need to determine the genotype of each parent.
Let's represent the S allele for smooth pods as S and the s allele for pinched pods as s.
The first parent has the genotype Ss, which means it has one allele for smooth pods (S) and one allele for pinched pods (s).
The second parent also has the genotype Ss, with one allele for smooth pods (S) and one allele for pinched pods (s).
To construct the Punnett square, we write the possible combinations of alleles that can be contributed by each parent along the top and left side of the square, respectively:
| S | s |
-----------------------------
S | SS | Ss |
-----------------------------
s | Ss | ss |
-----------------------------
Each box in the Punnett square represents a possible genotype of the offspring, obtained by combining one allele from each parent.
Now, let's determine the phenotype of each genotype. Since the allele for smooth pods (S) is dominant over the allele for pinched pods (s), individuals with the genotype SS or Ss will have smooth pods. Only individuals with the genotype ss will have pinched pods.
Out of the possible genotypes in the Punnett square, 3 out of 4 have at least one S allele (SS, Ss, Ss), which means they will have smooth pods. This is 75% of the offspring.
Therefore, the correct answer is 75%.