A recessive gene is a gene variant that only shows its effect if an individual has two copies of the allele, one from each parent, which is also known as being homozygous. In other words, a recessive trait is expressed only when the genotype is homozygous. Individuals inherit two versions of each gene, known as alleles, from each parent. In the case of a recessive trait, the alleles of the trait-causing gene are the same, and both (recessive) alleles must be present to express the trait. If only one copy of the recessive allele is present, it does not produce a trait at all. Recessive genes are often associated with genetic disorders, and carriers of a recessive gene have one gene copy with a problem but have enough leftover function from the other copy for normal cell function.