Which of the following best describes the concept of dominance in genetics?

The concept of dominance in genetics is best described as one allele masking the effect of another allele. This means that when two different alleles for a particular gene are present in an individual, the dominant allele will typically overpower the expression of the recessive allele. Consequently, the phenotype of the organism reflects the trait associated with the dominant allele rather than that of the recessive allele.

In cases of dominance, the presence of a dominant allele leads to its trait being expressed, regardless of whether the individual has one or two copies of that dominant allele. For example, if a dominant allele is indicated by a capital letter (like "A") and the recessive by a lowercase letter (like "a"), an individual with either "AA" or "Aa" genotypes will display the dominant trait, effectively masking the influence of the recessive allele.

The other choices provide different concepts that do not accurately represent the definition of dominance. The equal expression of both alleles describes a situation known as co-dominance or incomplete dominance, whereas a recessive trait appearing refers to cases when the dominant allele is absent. Lastly, the combination of multiple alleles suggests polygenic inheritance or multiple allelic traits, which also does not pertain specifically to the concept of dominance