Final answer:
A dominant trait is seen in a heterozygous organism (Option B), where only one of the two different alleles for a gene needs to be dominant for the trait to be expressed in the phenotype. It is not necessarily the most common trait nor one that confers a selective advantage.
Step-by-step explanation:
Understanding Dominant Traits
The term dominant trait refers to a phenotypic characteristic that is observable in an individual carrying two different alleles for a particular gene, where one is dominant and the other recessive. In the context of classical genetics, this most accurately fits the description that a dominant trait is one seen in a heterozygous organism (Option B). When observing a trait that is determined by one dominant and one recessive allele, like in the case of flower color where violet is dominant and white is recessive, the presence of the dominant allele 'A' in combination with the recessive allele 'a' will result in the phenotype displaying the dominant trait, regardless of whether the genotype is homozygous dominant (AA) or heterozygous (Aa).
Mendel's work with peas illustrated the principle of dominance, where he crossed plants with different traits and observed that certain characteristics (dominant traits) appeared in the F1 generation, while others (recessive traits) appeared only when both alleles were recessive and were present in the F2 generation upon further breeding.
It is important to dispel common misconceptions: a dominant trait is not necessarily the most common in a population nor does it confer a selective advantage. Dominance in genetics is purely a matter of which allele masks the other in terms of phenotypic expression.