What is incomplete dominance?

Incomplete Dominance

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a third phenotype that is a blend of the parental traits.

Here's a breakdown of key aspects:

• Phenotype: The heterozygous genotype produces an intermediate phenotype that is distinct from either homozygous phenotype. This is the defining characteristic. Instead of one allele masking the other, their effects are combined.

• Genotype: Genotypic ratios in the offspring remain consistent with typical Mendelian inheritance patterns. For instance, in a monohybrid cross (Aa x Aa), you'll still observe a 1:2:1 genotypic ratio (AA:Aa:aa). However, the phenotypic ratio will also be 1:2:1 because each genotype produces a distinct phenotype.

• Examples: A classic example is the flower color in snapdragons. When a homozygous red flower (RR) is crossed with a homozygous white flower (WW), the offspring (RW) are pink. Neither red nor white is dominant, so the resulting color is a blend. Another example is the color of feathers in certain breeds of chickens.

• Contrast with Complete Dominance: Unlike complete dominance, where the dominant allele completely masks the recessive allele in heterozygotes, incomplete dominance results in a clearly different phenotype.

• Not Blending Inheritance: It's important to distinguish incomplete dominance from the outdated concept of blending inheritance. In incomplete dominance, the genes themselves don't blend. The heterozygote produces an intermediate phenotype because neither allele fully masks the other. If you cross two heterozygous offspring, the original parental phenotypes will reappear in the next generation.