What defines autosomal dominant genetic disorders?

Autosomal dominant genetic disorders are defined by the requirement that an individual must inherit at least one dominant allele for the trait to exhibit the disorder. This means that if one parent carries the dominant allele for the disorder, there is a 50% chance that the offspring will inherit that allele and, consequently, display the characteristics of the disorder.

The nature of dominant alleles is such that they can mask the effects of recessive alleles. Therefore, only one copy of the dominant allele is needed for the trait to manifest, which is a key characteristic distinguishing autosomal dominant disorders from autosomal recessive disorders, where two copies of the recessive allele are necessary for expression.

In contrast, the other options do not accurately reflect the behavior of autosomal dominant traits. One option suggests that both alleles must be recessive for expression, which pertains to autosomal recessive disorders rather than dominant ones. Another option incorrectly states that only females are affected, whereas autosomal dominant disorders can affect individuals of any sex. Lastly, the idea that these disorders are expressed only in the presence of two dominant alleles misunderstands the fundamental principle of dominance in genetics, which clearly emphasizes that a single dominant allele is sufficient for expression.