Which of the following represents a trait that is not expressed in the presence of a dominant allele?

The trait that is not expressed in the presence of a dominant allele is referred to as recessive. In Mendelian genetics, alleles can be categorized as dominant or recessive based on their expression. A dominant allele will mask the expression of a recessive allele when both are present in a heterozygous genotype. This means that for a recessive trait to be phenotypically observable, the individual must have two copies of the recessive allele, or be homozygous for that trait.

For instance, if we consider a gene involved in flower color where purple (P) is the dominant allele and white (p) is the recessive allele, a plant with the genotype Pp (one dominant and one recessive allele) will display purple flowers, while a plant with the genotype pp will show white flowers.

In contrast, dominant alleles express their traits regardless of the presence of other alleles, codominant alleles express both traits distinctly in a heterozygote, and polygenic traits involve multiple genes contributing to a single phenotype. Therefore, the correct identification of the recessive trait is essential for understanding Mendelian inheritance patterns.