Incomplete dominance

Incomplete Dominance is a genetic phenomenon where neither of the two versions of a gene is completely dominant over the other. This results in a third phenotype, where the expressed physical trait is a combination of the phenotypes of both alleles. Unlike complete dominance where one allele is completely dominant over the other, incomplete dominance results in a phenotype that is a mixture of the parent phenotypes.

Overview

Incomplete dominance occurs when the phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. For example, if a white flowered plant (WW) is crossed with a red flowered plant (RR), the offspring will be pink (WR).

Examples

One classic example of incomplete dominance is the color of the snapdragon flower. When a red-flowered snapdragon (RR) is crossed with a white-flowered snapdragon (WW), the result is not a red or white flower, but a pink snapdragon (WR).

Another example is found in certain breeds of chickens. When a chicken with black feathers (BB) is crossed with a chicken with white feathers (WW), the resulting offspring have a coloration described as blue (BW).

Genetic Basis

The genetic basis of incomplete dominance is related to the inability of one allele to produce enough functional protein to exhibit a dominant phenotype. This can occur if the dominant allele is a loss-of-function allele, or if the protein it produces is not fully functional.

See Also

• Genetics
• Dominance (genetics)
• Codominance
• Mendelian inheritance

References

Incomplete dominance Resources
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