Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards. To unlock all 5, videos, start your free trial. In both codominance and incomplete dominance , both alleles for a trait are dominant. In codominance a heterozygous individual expresses both simultaneously without any blending.
An example of codominance is the roan cow which has both red hairs and white hairs. In incomplete dominance a heterozygous individual blends the two traits.
An example of incomplete dominance is the pink snapdragon, which receives a red allele and white allele. While most students get the idea between a dominance and recessive alleles what often throws them for a curve is the difference between codominance and Incomplete Dominance, so let's take a closer look at those, so these are exceptions to the whole idea about complete dominance where one allele will completely overwhelm or not allow the other alleles effects to be shown.
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Codominance is a concept in which heterozygous offspring produces both alleles simultaneously without any mixing of the two parental alleles. In codominance, both parental alleles are dominantly expressed in the offspring.
Both parental alleles can be observed in the offspring without blending. Thus, codominance is a qualitative approach of gene expression. Codominance mostly occurs when more than two alleles are present for the determination of the phenotype of a particular trait.
Those alleles are called multiple alleles. Figure 1: Hybrid Red and White Camellia. The roan cow containing both red and white hairs is an example of codominance. The AB blood group also shows codominance in humans. A cross between the red homozygous Camellia flowers and white homozygous Camellia flowers produces an offspring with both red and white spots within the same flower is shown in figure 1.
Google Classroom Facebook Twitter. Video transcript - [Voiceover] So today we're gonna talk about Co-Dominance and Incomplete Dominance, but first let's review the example of a blood type and how someone with the same two alleles coding for the same trait would be called homozygous and someone with different alleles would be called heterozygous. Also remember, the concept of dominant and recessive alleles and how the A allele is dominant over the O allele in this example.
This means that the same phenotype, blood type A, can result from these two different genotypes. Now, the example that I just gave you was an example of Complete Dominance.
So if a person had a genotype AO, since our phenotype is just blood type A, it means that the A allele is completely dominant over the O allele and only the A allele from the genotype is expressed in the phenotype. But there are actually three different patterns of dominance that I want you to be familiar with and to explain this I'm going to use a different example.
Let's say we have this flower and the red petal phenotype is coded for by the red R allele and the blue flower phenotype is coded for by the blue R allele. So I'm going to introduce three different patterns of dominance and they are complete dominance, which you've already heard of, co-dominance, and also incomplete dominance.
I'm going to explain what these two new patterns are through this flower example.
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