Many people mistakenly think incomplete dominance and codominance are the same. They are in fact, different examples of non-Mendelian genetics.
With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits. Incomplete dominance is also called partial dominance.
What happens when you mix equal amounts of black paint and white paint? What color do you get? Click on the image below to find out.
Incomplete dominance is like the blending of the paint colors.
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With codominance, a cross between organisms with two different phenotypes produces offspring with both alleles being expressed equally. The traits do not blend but instead are expressed together. The prefix "co" means together.
Codominance is like a tie-dyed shirt.
Source: How to Tie Dye a White T-shirt, Wiki How
Both the original color of the shirt and the color of the dye placed on the shirt appear.
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Let’s summarize the difference between incomplete dominance and codominance.