Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant characteristic.

The flower color trait in radishes is an example of which of the following?

A) a multiple allelic system

B) sex linkage

C) codominance

D) incomplete dominance

E) epistasis

The answer is D) incomplete dominance.

Incomplete dominance occurs when heterozygous phenotype is intermediate to the dominant homozygous and recessive homozygous phenotypes. In radish flowers, purple is intermediate to white and red flowers. So, purple color is characteristic for heterozygous phenotypes. When dominant red flowers are crossed with recessive white flowers, all offspring will be heterozygotic and with intermediate - purple color.