What defines a recessive allele in the context of inheritance?

A recessive allele is specifically characterized by the requirement that two copies of it must be present for the trait it codes for to be expressed phenotypically. This means that if an individual has only one copy of the recessive allele and one copy of a dominant allele, the dominant allele will determine the organism’s visible traits, effectively masking the expression of the recessive one.

In terms of inheritance patterns, recessive alleles are typically observed in the offspring only when inherited from both parents. For example, if a gene has one dominant allele (let's say, "A") and one recessive allele ("a"), the phenotype will display the dominant trait when the genotype is either "AA" or "Aa." The recessive trait associated with the "aa" genotype will only be visible when no dominant alleles are present.

Other definitions presented do not accurately capture the nature of recessive alleles. For instance, dominant alleles are the ones that mask the expression of recessive alleles, while the commonality of an allele in a population does not define its recessive status. Furthermore, not all alleles guarantee a specific phenotype, especially recessive ones, as their effect is only seen in a homozygous state. Therefore,