Which statement is true regarding dominant alleles?

Dominant alleles can indeed arise from both gain of function mutations and loss of function mutations. A loss of function mutation can lead to a situation where the remaining functional copy of a gene is sufficient to ensure the phenotype is expressed, making that allele dominant over the recessive one. For example, in some cases, a dominant allele may produce a non-functional protein leading to a phenotype that is expressed because the activity of the other gene copy does not sufficiently compensate for the loss.

This understanding is crucial in genetics because it highlights that the expression of dominant traits is not solely tied to enhancing functions (gain of function) but can also occur under conditions where there is a reduction or complete loss of a normal function that results in the dominant trait being exhibited. This perspective is essential when studying inheritance patterns and genotype-phenotype correlations in various organisms.