What effect does a dominant allele have in a genetic cross?

A dominant allele plays a crucial role in determining the phenotype, or observable traits, of an organism when it is present in the genotype. When a dominant allele is present alongside a recessive allele, it masks the effects of the recessive allele. This means that the traits associated with the dominant allele will be expressed, while those associated with the recessive allele will not be visible in the phenotype.

For instance, if we consider a situation where one allele codes for brown eyes (dominant) and another for blue eyes (recessive), an organism with at least one brown eye allele will exhibit brown eyes, effectively masking the effect of the blue eye allele. This characteristic is essential in understanding inheritance patterns and predicting phenotypic outcomes in offspring from genetic crosses.

In contrast, choices that imply the dominant allele results in a recessive phenotype, allows the recessive allele to express itself, or has no impact on phenotype do not align with the established principles of Mendelian genetics. These descriptions misrepresent the role of dominant alleles in inheritance.