In a genetic cross, how is a phenotype determined?

The correct choice highlights that a phenotype is determined by the interaction of both alleles present in an individual. In genetics, a phenotype refers to the observable traits or characteristics of an organism, which result from the expression of genes. Each individual carries two alleles for a given gene, one inherited from each parent.

When discussing inheritance, particularly in the context of Mendelian genetics, it is crucial to understand that alleles can be dominant or recessive. The dominant allele often masks the effect of the recessive allele when both are present. However, the phenotype is not solely dictated by the more dominant allele; rather, it is a result of the combined influence of both alleles and how they interact. This interaction can lead to various expressions of traits, including complete dominance, incomplete dominance, or codominance.

For instance, in cases of incomplete dominance, the phenotype may represent a blend of the traits associated with both alleles. In codominance, both alleles contribute equally and visibly to the phenotype. Therefore, recognizing that both alleles interact helps in understanding the complexity of phenotypic expression and the variety of traits that can arise from different combinations of alleles. This comprehensive view aligns well with principles of inheritance and gene expression.