What role do recessive alleles play in genetics?

Recessive alleles play a crucial role in genetics by being expressed in the phenotype only when two copies are present. This means that for a recessive trait to be visible in an organism's physical appearance, the organism must inherit copies of the recessive allele from both parents. If an individual has just one recessive allele along with a dominant allele, the dominant trait will be expressed instead, masking the effect of the recessive allele.

This concept is fundamental in understanding inheritance patterns, as it shows how traits can be carried in a population without being immediately visible. The presence of recessive alleles can contribute to genetic diversity and can re-emerge in future generations when offspring inherit two copies of the recessive allele. This phenomenon is particularly relevant in analyzing family pedigrees and predicting the likelihood of certain traits appearing in offspring.