The term "incomplete dominance" refers to a genetic pattern where neither of two alleles is completely dominant over the other. When these alleles interact, the phenotype produced is a mix of the two, with neither allele completely overpowering the other. The spelling of "incomplete dominance" can be broken down phonetically as /ɪnkəmˈpliːt doʊmɪnəns/. This can be understood as "in-kum-pleet doh-muh-nuhns," where each symbol represents a specific sound in the English language.
Incomplete dominance is a genetic phenomenon characterized by the blending of two different alleles, resulting in an intermediate phenotype that is not completely dominant or recessive. This means that neither allele completely masks the expression of the other, thereby creating a new third phenotype.
In cases of incomplete dominance, the heterozygous genotype exhibits a distinct phenotype that is different from both homozygous genotypes. For example, if a red-flowered plant (RR) is crossed with a white-flowered plant (WW), the resulting offspring (RW) will have pink flowers, which is a blending of the red and white phenotypes.
The underlying mechanism of incomplete dominance lies in the incomplete expression of the dominant allele. Unlike complete dominance, where one allele fully masks the other, both alleles contribute to the phenotype in incomplete dominance. This may occur due to a partial loss of function in the dominant allele, resulting in a reduction of its phenotypic effect. As a result, a blending effect occurs, leading to the expression of an intermediate phenotype.
Incomplete dominance is commonly observed in traits such as flower color, hair texture, and pigment production. It is important to note that incomplete dominance does not imply a lack of dominance; instead, it represents a unique gene expression pattern where neither allele is completely dominant or recessive over the other.
The term "incomplete dominance" was coined by the American geneticist William E. Castle in 1913. The word "incomplete" refers to the idea that the dominant allele does not completely mask or overpower the effects of the recessive allele. Instead, both alleles contribute to the resulting phenotype, resulting in an intermediate or blended phenotype. The concept of incomplete dominance emerged through Castle's work on flower color inheritance in snapdragons, where he observed that crossing a red-flowered variety with a white-flowered variety produced pink-flowered offspring.