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.

Key Concepts

Recessive Alleles

Recessive alleles are variants of a gene that do not manifest their traits in the presence of a dominant allele. In a heterozygous individual, where one allele is dominant and the other is recessive, the dominant trait is expressed, while the recessive trait is masked. This is why the pea wrinkle-seed allele is considered recessive; it only appears phenotypically when an individual is homozygous for the recessive allele.

Homozygous vs. Heterozygous

An organism is homozygous for a trait when it has two identical alleles, either dominant or recessive, while it is heterozygous when it has one of each. In the context of the pea wrinkle-seed allele, homozygous recessive individuals express the wrinkled phenotype, whereas heterozygous individuals, carrying one dominant allele, will display the dominant phenotype, thus obscuring the recessive trait.

Mendelian Inheritance

Mendelian inheritance refers to the patterns of inheritance first described by Gregor Mendel, which include the principles of dominance, segregation, and independent assortment. According to these principles, traits are inherited independently, and dominant alleles can mask the expression of recessive alleles in heterozygous conditions, leading to predictable ratios of traits in offspring, such as those observed in the F2 generation of pea plants.