What does dominance refer to in genetics?

Dominance in genetics refers specifically to a situation where one allele masks or suppresses the expression of another allele at the same locus. This occurs when an organism is heterozygous for a trait, meaning it possesses two different alleles. In this context, the dominant allele will be expressed in the phenotype, while the recessive allele will not be observable. For example, in pea plants, the allele for tall stems is dominant over the allele for short stems, so if a plant has one of each allele, it will display the tall phenotype.

Understanding the concept of dominance is crucial in predicting inheritance patterns, such as those described by Mendel's laws. It helps explain why certain traits appear more frequently in offspring when one parent contributes a dominant allele. The other choices do not accurately capture the meaning of dominance. The idea of a trait being common in a population relates more to frequency rather than dominance. Visible traits suggest co-dominance or incomplete dominance rather than simple dominance. Lastly, the notion of alleles competing equally would imply a scenario of co-dominance, where both alleles contribute to the phenotype rather than one masking the other.