When two different alleles are present, which one is typically expressed?

When two different alleles are present for a particular gene, the typical expression is that of the dominant allele. Dominance refers to the relationship between alleles in which one allele masks or suppresses the expression of another. In this case, the dominant allele will determine the phenotype, or observable characteristics, of an organism.

The dominant allele is usually represented by a capital letter, while the recessive allele, which does not manifest in the presence of the dominant allele, is represented by a lowercase letter. For example, if we consider a gene for flower color, where 'R' represents the dominant red color and 'r' represents the recessive white color, a plant with the genotype 'Rr' would display red flowers because the dominant 'R' allele is present.

In contrast, the recessive allele will only be expressed in the phenotype when two copies of the recessive allele are present (homozygous condition). Additionally, in cases of co-dominance or incomplete dominance, both alleles may contribute to the phenotype in unique ways, such as mixed colors or a blend, but these scenarios are not typical of simple dominance.

Thus, when considering the basic principles of Mendelian inheritance, the presence of a dominant allele is what typically