What is the definition of a dominant trait?

A dominant trait is defined as a trait that is expressed regardless of the second allele. This means that if an individual possesses at least one dominant allele for a particular trait, that trait will manifest in the organism's phenotype. For example, if we consider a gene with two alleles: one dominant (let's say "A") and one recessive (like "a"), an individual with the genotype "AA" (homozygous dominant) or "Aa" (heterozygous) will display the dominant trait. It does not matter if the second allele is dominant or recessive; the presence of just one dominant allele is sufficient for the trait to be observed.

This defining characteristic of dominance is crucial in genetics, as it helps explain how traits can be inherited and expressed across generations. In contrast, a recessive trait would only be expressed when an individual has two copies of the recessive allele (homozygous recessive). Inheritance patterns and the relationship between dominant and recessive alleles are fundamental concepts in studying genetics and heredity.