Diving Deeper
Before Mendel came along, many people thought that by breeding two organisms with certain traits, the two traits would mix or both show. We now know that this also happens in addition to simple Mendelian genetics. These different types of inheritance are called inheritance patterns.
Codominance
When the alleles are different but there is no dominant or recessive allele, the phenotypes of both alleles are expressed in a third phenotype. For example: All the offspring of these two flowers are mixed red/white, or spotted, a phenotype that includes both of the parents’ (but not blending them.) This is called Codominance—both phenotypes are present.
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Incomplete Dominance
Another inheritance pattern is called Incomplete Dominance—when both phenotypes mix. A cross between organisms with two different alleles that follow this pattern produces offspring with a phenotype that blends together the parental phenotypes. For example, all the offspring of these two flowers (1 Homozygous red, 1 homozygous white) turn out to be pink—a mixture of the two phenotypes. Although the genotypes look similar to that of codominance, the phenotype is a blending of the two phenotypes rather than both phenotypes existing together. It is 100% RW (pink).
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