According to modern genetics, which statement about dominant traits is true?

The assertion that dominant traits can be expressed simultaneously with another trait is grounded in the principles of incomplete dominance and co-dominance, which are concepts in modern genetics that expand upon the traditional understanding of dominant and recessive alleles. In cases of incomplete dominance, a blend of traits occurs, resulting in a phenotype that is different from both homozygous dominant and homozygous recessive phenotypes. Co-dominance, on the other hand, allows both traits to be fully expressed at the same time, as seen in the case of AB blood type, where both A and B alleles are expressed in individuals with that genotype.

This coexistence of traits illustrates that dominant traits are not necessarily exclusive in expression, allowing for a more complex interaction between alleles than the simplistic dominant-recessive model suggests. Therefore, the correct answer reflects an advanced understanding of genetic interactions beyond basic dominance, highlighting the nuance of genetic expression.