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Current time:0:00Total duration:3:29

Video transcript

so today we're going to talk about codominance and incomplete dominance but first let's review the example of 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 el eel 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 le o 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 so 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 codominance and also incomplete dominance and I'm going to explain what these two new patterns are through this flower example so let's start by looking three different genotypes and the phenotypes that you would see for each of them under each different dominance pattern so we'll start with the genotype - red ours which we can expect that in all cases the flower petals will be red since we only have red ours in the genotype similarly if our genotype had two blue ours then we can expect that in all cases the flower petals will be blue since we only have blue ours in the genotype now these three different dominance patterns change when we look at the heterozygous example and that's what makes these three patterns different now we're already familiar with the example of complete dominance so if we said that the red R is dominant over the blue R then this would make the heterozygous phenotype or flower for complete dominance now what codominance is is when the heterozygous phenotype shows a flower with some red petals and some blue petals so it's when the two alleles are dominant together they are codominant and traits of both alleles show up in the phenotype now what incomplete dominance is is when the heterozygous phenotype shows a mixture of the two alleles so in this case the red and blue flower petals may combine to form a purple flower neither allele is completely dominant over the other and instead the to being incompletely dominant mixed together so what did we learn well if we assume the heterozygous genotype red or blue are then there are three different dominance patterns that we might see for a specific trait incomplete dominance only one allele in the genotype of the dominant allele is seen in a phenotype and this was the example with the red flower in codominance both the alleles in the genotype are seen in the phenotype and this was the example with the flower with both red and blue petals and finally an incomplete dominance a mixture of the alleles in the genotype is seen in the phenotype and this was the example with the purple flower
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