Why is the pea wrinkle-seed allele a recessive allele? a. It 'recedes' in the F2 generation when homozygous parents are crossed. b. The trait associated with the allele is not exhibited in heterozygotes. c. Individuals with the allele have lower fitness than that of individuals with the dominant allele. d. The allele is less common than the dominant allele. (The wrinkled allele is a rare mutant.)

Verified step by step guidance

1. Understand the concept of dominant and recessive alleles: Dominant alleles are expressed in the phenotype even if only one copy is present (heterozygous), while recessive alleles are only expressed when two copies are present (homozygous).
2. Review the options given in the question and relate them to the definitions of dominant and recessive alleles.
3. Option b states that the trait associated with the allele is not exhibited in heterozygotes. This means that the presence of a dominant allele masks the expression of the recessive allele in heterozygous individuals.
4. Analyze the other options: a refers to the behavior in a generation, c involves fitness which is not directly related to the definition of recessiveness, and d discusses allele frequency which also does not determine recessiveness.
5. Conclude that the correct answer is b because it directly describes the fundamental characteristic of a recessive allele, which is not being expressed in the presence of a dominant allele in heterozygous individuals.