Dominant trait

A heritable characteristic expressed when an individual carries at least one allele that produces it, including in a heterozygotes. Dominance describes how alleles relate in a particular context, not how common or advantageous a trait is.

Allele: One of two or more alternative forms of a gene at a particular genomic location. A dominant trait appears when at least one allele contributes to its expression.
Gene: A DNA sequence that contributes to a functional product or regulates its production. Alleles of a gene can produce different versions of a heritable characteristic.
Recessive trait: A heritable characteristic expressed under a specified allele relationship when the relevant recessive allele combination is present. It is often masked in heterozygotes by a dominant allele.
ABO blood group system: A human blood-group system determined chiefly by A, B, and O alleles of the ABO gene. A and B alleles are codominant, while each is dominant over O.
Autosomal dominant inheritance: Inheritance in which one altered allele on a non-sex chromosome can cause a trait or disorder. It is a common inheritance pattern for traits expressed with one contributing allele.
Heterozygote: An organism or cell with different alleles at a genetic locus. A dominant allele can determine the phenotype even when paired with a different allele.
Homozygote: An organism or cell with identical alleles at a genetic locus. Comparing homozygotes with heterozygotes helps reveal an allele’s dominance relationship.
Allele frequency: The proportion of gene copies in a population represented by a particular allele. A dominant trait can be rare; dominance does not determine population frequency.
Huntington disease: An inherited neurodegenerative disorder commonly caused by an expanded CAG repeat in the HTT gene. One disease-associated allele can be sufficient for the characteristic autosomal dominant inheritance pattern.
Genetic counseling: A clinical process that helps people understand genetic conditions, testing, and reproductive options. Dominant inheritance patterns can inform estimates of familial risk.

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