Partial dominance

Partial dominance is a concept in genetics that describes the relationship between two alleles of a single gene where the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes. This phenomenon is also referred to as incomplete dominance. It contrasts with complete dominance, where the phenotype of the heterozygote is identical to the phenotype of one of the homozygotes, and codominance, where the phenotypes of both alleles are fully expressed in the heterozygote.

Overview

In partial dominance, the phenotype of the heterozygote is a blend or an intermediate of the phenotypes of the homozygotes. For example, in the case of flower color in certain species of plants, if the allele for red flowers (R) shows partial dominance over the allele for white flowers (r), the heterozygote (Rr) will have pink flowers. This is because the allele for red flowers does not completely mask the effect of the allele for white flowers, leading to an intermediate phenotype.

Genetic Mechanism

The genetic mechanism behind partial dominance involves the level of expression of the alleles involved. In many cases, the allele with partial dominance does not produce enough of a particular protein to generate the same phenotype as in the homozygous dominant condition. As a result, the phenotype of the heterozygote is a diluted version of the dominant phenotype.

Examples

One of the classic examples of partial dominance is the flower color in the snapdragon (Antirrhinum majus). As mentioned, when a red-flowered plant is crossed with a white-flowered plant, the offspring (F1 generation) have pink flowers. Another example can be found in the coat color of certain breeds of animals, where the heterozygote exhibits a color that is intermediate between the colors of the homozygous individuals.

Implications

The concept of partial dominance has significant implications in the fields of genetics, evolution, and breeding. Understanding how partial dominance works can help geneticists predict the outcome of crosses between individuals with different genotypes. It also plays a role in evolutionary biology, as it affects the variation and adaptation of traits within populations. In breeding, knowledge of partial dominance can be used to achieve desired phenotypes in plants and animals.

See Also

• Genotype
• Phenotype
• Dominance (genetics)
• Codominance
• Mendelian inheritance