Use in clinical context
With the exception of the sex chromosomes in males, individuals have two copies of each gene and both can contribute to the phenotype. If a variant is recessive both copies need to be the same for the phenotype to be expressed. Even when two copies of a recessive variant are present, expression can still be influenced by other factors. This can result in the phenotype not being expressed or different forms of phenotype presentations despite the presence of two copies of the recessive variant.