In terms of genetic expression, what does “dominance” typically refer to?

Dominance in genetics specifically refers to the ability of one allele to mask the effect of another allele at the same locus. When an organism has two different alleles for a trait, the dominant allele is the one that determines the phenotype, while the recessive allele's effects are concealed. This characteristic is fundamental to understanding inheritance patterns, as it explains why certain traits appear in offspring even when one of the alleles is recessive.

For instance, if a pea plant has one allele for purple flowers (dominant) and one for white flowers (recessive), the plant will exhibit purple flowers because the purple allele masks the expression of the white allele. This concept is crucial in Mendelian genetics, where dominant and recessive alleles can lead to predictable patterns in traits across generations.

The other options describe different concepts that do not align with the definition of dominance. Equal expression of both alleles pertains more to co-dominance or incomplete dominance, while a complete lack of gene expression does not apply in this context. Hybrid vigor refers to the enhanced biological qualities often seen in crossbreeds, which is unrelated to the dominance of alleles.