Which description fits a dominant allele?

A dominant allele is defined by its ability to manifest its trait in both homozygous (where the individual has two identical alleles for a trait) and heterozygous conditions (where the individual has one dominant allele and one recessive allele). This means that when a dominant allele is present, it will always express its associated trait, even if paired with a recessive allele.

In contrast, a recessive allele requires both alleles to be recessive (homozygous condition) for its trait to be expressed. Therefore, the defining characteristic of a dominant allele is that its influence on phenotype can be observed regardless of whether the organism possesses one or two copies of that allele.

The other options describe characteristics that do not align with the fundamental definition of a dominant allele. For instance, dominant alleles can be associated with genetic disorders, but this is not a defining feature of all dominant alleles. Similarly, the phenomenon of affecting only male offspring pertains to sex-linked traits, which is unrelated to the categorization of an allele as dominant or recessive.