What is an incomplete dominance '?

Answer 1

A good example of incomplete dominance is the color of Japanese 4 o'clock flowers. A red Japanese 4 o'clock will have the genotype RR. A white Japanese 4 o'clock will have the genotype WW.

When these two flowers are crossbred, each will give one of their genes. The red flower will give a R (for red) gene. The white flower will give a W (for white) gene. The offspring will have the genotype RW.

Since neither of these are recessive, (recessive genes have lower case letters) they both show up in the phenotype. The result is a mix of red and white: pink flowers!

Had the white gene been recessive, and the offspring had the genotype Rw, then the flower would be red. Since both are dominant, they have incomplete control of the phenotype.