What is indicated by a phenotype that expresses a recessive trait?

A phenotype that expresses a recessive trait indicates that the individual is homozygous recessive for that trait. This means that both alleles inherited from the parents for that particular gene are the recessive form. For a recessive trait to be visibly expressed in the phenotype, the dominant allele must be absent, which occurs when the organism carries two copies of the recessive allele.

This understanding is rooted in the principles of Mendelian genetics, where traits are determined by alleles - the versions of a gene. If a trait is recessive, it will only manifest when an individual has two recessive alleles (homozygous recessive). In contrast, if the individual is homozygous dominant, only the dominant trait would be present. A heterozygous individual, possessing one dominant and one recessive allele, would also not express the recessive trait, as the dominant allele would mask its effects. Co-dominance refers to a situation where both alleles in a heterozygote are fully expressed, leading to a phenotype that shows characteristics of both alleles, which does not pertain to recessive traits.

Therefore, the manifestation of a recessive phenotype confirms the homozygous recessive genotype is the accurate conclusion