Recessive trait

An inherited characteristic expressed when no dominant allele masks the associated recessive allele. Its expression depends on genotype and, in some cases, interactions among genes and environment.

Allele: One of the alternative forms of a gene or other genomic sequence at a particular location. A recessive trait arises from how particular alleles combine and function.
Homozygosity: The state of carrying identical alleles at a particular genetic locus. Two recessive alleles at a locus commonly permit expression of the trait.
Cystic fibrosis: An inherited disorder caused by pathogenic variants in both copies of the CFTR gene. It is a well-known example of an autosomal recessive condition.
Dominant trait: An inherited characteristic expressed when a dominant allele is present under a specified genetic model. It contrasts with a recessive trait that is masked in many heterozygotes.
Autosomal recessive inheritance: Inheritance of a condition caused by relevant variants in both copies of a gene on an autosome. This is the common inheritance pattern behind many recessive traits and disorders.
Genotype: The genetic constitution of an organism, or the alleles it carries at specified loci. The allele combination determines whether the trait is expressed.
Heterozygosity: The state of carrying different alleles at a particular genetic locus. A heterozygote often carries a recessive allele without showing its associated trait.
Phenylketonuria: An inherited metabolic disorder in which impaired phenylalanine breakdown can cause toxic accumulation. Its usual inheritance pattern is autosomal recessive.
Incomplete dominance: An inheritance pattern in which a heterozygote has a phenotype intermediate between those of the two homozygotes. Neither allele fully masks the other, unlike simple complete dominance.
X-linked recessive inheritance: Inheritance of a condition caused by a recessive variant in a gene on the X chromosome. A single affected X-linked allele can produce a trait in individuals with one X chromosome.

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