What is incomplete dominance?

Answer 1

Incomplete dominance is where the phenotype of the heterozygote is intermediate to both the heterozygotes. The classic example of this phenomenon is pink snapdragons. If you cross red and white snapdragons, you get pink snapdragons, because neither the red or white allele is dominant to the other.

Answer 2

In the realm of genetics. In diploid 'creatures' there are two allenes for every trait. These can be expressed as AA BB CC DD etc. Sometimes there are more than one gene for an allene. In the simple two gene case we can express this as 'A' and 'a'. For a diploid creature then there are four possible combination of genes for a particular allene:

AA Aa aA AA.

For all particle purposes aA and Aa are the same thing.

Different genes often give different traits to the phenotypes of the creature so an AA creature would be different in one trait than an AA relative. Often the hybred creature Aa will have one gene dominate (express its trait solely). We consider this the A gene for convenience and call it the dominate gene. The a gene therefore will only get expressed when it is in the configeration AA and is called the recessive gene.

Sometimes there is imcomplete dominance. this means that there is a third expression of the trait, associated with the Aa hybred. This expression is usually half-way to the dominate form.

For example with the gentic condition syckle cell anemia the dominate form AA is condition free but are susceptible to malaria infection. The recessive form AA has a uncomfortable blood condition. The hydred Aa is condition free and is immune to malaria.