Incomplete dominance means that neither allele is fully dominant over the other. Instead of one allele completely masking the other, they both contribute to the phenotype.
Think of it like this:
* Dominant allele: Imagine a red paint color.
* Recessive allele: Imagine a white paint color.
* Incomplete dominance: Instead of getting red or white, you get a mix – pink!
Why it's not a true blend:
* Alleles remain distinct: The alleles for the red and white colors are still present in the offspring. They haven't merged or disappeared.
* Different expression: The pink phenotype arises because the alleles are expressed at a different level than in homozygous individuals. The red allele may be producing less red pigment, while the white allele isn't producing any white pigment, leading to a combination that appears pink.
The Appaloosa horse example:
In Appaloosa horses, the coat pattern is influenced by incomplete dominance. A homozygous horse with two copies of the "leopard" allele will have a full leopard coat, while a homozygous horse with two copies of the "solid" allele will have a solid coat.
A heterozygous horse with one "leopard" and one "solid" allele will have a "blanket" coat pattern, which is a blend of leopard spots and solid color. But again, this blending is just an appearance – the underlying alleles are still separate and distinct.
Key takeaway:
Incomplete dominance is not a true blend of alleles. It's about the different levels of expression of two alleles, leading to a phenotype that is intermediate between the homozygous phenotypes.
