What role does dominance play in genetics?

Dominance in genetics refers to the relationship between alleles of a gene and how they influence the phenotype, or observable characteristics, of an organism. The correct choice highlights that the presence of just one dominant allele is sufficient for the expression of the dominant trait in the phenotype.

In genotype terms, an organism may have two different alleles for a trait, known as heterozygous, or it may have two of the same allele, known as homozygous. When one of these alleles is dominant, it can express its trait even when paired with a recessive allele. For instance, if we consider a gene controlling flower color where 'R' represents the dominant allele for red petals and 'r' represents the recessive allele for white petals, the presence of at least one 'R' (either 'RR' or 'Rr') results in red petals. This indicates that dominant alleles can mask the presence of recessive alleles in heterozygous individuals, leading to the observable expression of only the dominant trait.

In contrast, the incorrect options misinterpret the nature of genetic dominance. Stating that both alleles must be present for phenotype suggests that dominance has no role, which contradicts the very definition of dominant alleles