>Co-dom is a very special type of genetic event. The only one I can think of is blood type. If you had co-dom roses, 1 red and 1 white, you'd end up with red and white roses. Variegated might be the best word.

The word "codominant" came out of blood typing. Early on, human blood types A and B were determined to be codominant. If blood cells in an AB individual were variegated, then some cells would be type A, some type B, and either some or none type AB. But ALL of the blood cells have both A and B molecular configurations. So "variegated" is not the answer.

In the theoretical rose example, the codominant heterozygote has a red gene paired with a white gene. It has pink flowers. The white gene is producing a functional product that would result in a white rose. The red gene is also producing a functional product that would result in a red rose. And the mixture of the two products in the heterozygote would produce pink flowers.

In incomplete dominance, using our theoretical rose example, the incomplete dominant heterozygote has a red gene paired with a white gene. It also has pink flowers. The white gene makes a nonfunctional product that does nothing. The red gene makes a functional product that makes the flower red. But one red gene cannot make as much product as two red genes can. And the lesser amount of red produced by the heterozygote is the cause of the pink flowers.

In both codominance and incomplete dominance, the plant with two red genes makes red flowers. The plant with two white genes makes white flowers. And the heterozygote, the plant with a red gene paired with a white gene, makes pink flowers. The only way to really identify a given example is to get into the cell biochemistry. The breeding results are the same in both cases. And the biochemical data is usually lacking. Those are the two reasons why many people (including me) use the two terms interchangably. Though I usually use "codominant" because it contains fewer characters.

Paul Hollander

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