High school biology
Co-dominance and Incomplete Dominance
In genetics, there are 3 main dominance patterns: complete dominance (only one dominant allele appears in the phenotype), co-dominance (both alleles are visible in the phenotype), and incomplete dominance (a mix of alleles creates a new phenotype). These patterns help us understand how traits are passed down from one generation to the next. Created by Ross Firestone.
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- At3:08, can someone explain this in more detail, plz? What in the name of evolution is ‘Co-dominance’?!(8 votes)
- Although I am not exactly sure what you mean by "What in the name of evolution is co-dominance" It means that if there are two flowers, one red and one blue, if the alleles codominated, they would produce a flower with red and blue petals. This is different from incomplete dominance, because that is when the alleles blend, and codominance is when the alleles stay the same in the phenotype, but are both shown in the pheno and genotype. Hence in oth of these situations, neither allele is dominant or recessive.(9 votes)
- What about recessive alleles in the codominance or incomplete dominance. Will recessive alleles be reflective in the phenotype?(5 votes)
- When you have codominance, you don't have recessive alleles.(9 votes)
- what's the difference between complete and incomplete dominance(6 votes)
- codominance means you see both of the traits such as having a cow with black spots means it has white and black genes, incomplete dominance would be a mix of the traits like having a white and red flower make a pink flower. The pink flower would be incompletely dominant to red, but it still has traits of white.(3 votes)
- Why does co-dominance and incomplete dominance happen? Is it just chance?(3 votes)
- I'm not sure if these things just happen by chance...
Incomplete dominance can occur because neither of the two alleles is fully dominant over the other, or because the dominant allele does not fully dominate the recessive allele.
Co-dominance can occur because both the alleles of a gene are dominant, and the traits are equally expressed.(2 votes)
- Are tortoiseshell cats an example of co-dominance? They have a mixture of both black & white and ginger in their coats.(4 votes)
- Good guess, but that is actually due to something known as X-inactivation.
Tortoiseshell (and calico) patterns typically only show up in female cats heterozygous for an X-linked gene that controls orange pigmentation. Due to one of the "extra" X-chromosome being inactivated randomly in each cell of in the embryo some cells will have the "O" allele and make orange, while the other cells will have the "o" allele and not make orange.
You can learn more about X-inactivation§ on Khan Academy here:
The wikipedia article on tortoiseshell cats is a good place to learn more about this phenomenon:
§Note: However, the part on the tortoiseshell phenotype seems a bit oversimplified.(6 votes)
- AT3:08the Co-Dominance is defined in the video am I correct(6 votes)
- When we have incomplete dominance: both pigments encoded by both alleles are in the same cell, they blend and give a third intermediate phenotype. (1 same feather is blue: mix of black and white)
If it's codominance, both parental traits appear in the heterozygous offspring, both pigments encoded by both alleles are in the same cell, but they do not blend, they stay separate: one hair is red and one hair is white.
What makes pigments blend in the incomplete dominance (blue Andulisian fowl) but do not blend in the codominance (roan horse), what prevents pigments from blending in the codominance?
Thank you(6 votes)
- What happens if O is completely dominant over A instead?(4 votes)
- If you are talking about human blood types, this simply does not just happen.(1 vote)
- Aren't codominance and incomplete dominance not considered a part of mendelian genetics? Aren't they an example of non-mendelian genetics?(3 votes)
- correct- they are called non-mendelian Genetics. :)(1 vote)
- I'm here to say that this instructor is my favorite. The examples are perfect and make it all sound like English. Thank you!(3 votes)
- [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. Let's start by looking at three different genotypes and the phenotypes that you would see for each of them under each different dominance pattern. We'll start with the genotype, two red Rs, which we could expect that in all cases the flower petals will be red since we only have red Rs in the genotype. Similarly, if our genotype had two blue Rs then we could expect that in all cases the flower petals will be blue since we only have blue Rs in the genotype. Now these three different dominance patterns change when we look at the heterozygous example. 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 a red flower for complete dominance. Now what co-dominance 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 co-dominant 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 two, being incompletely dominant, mix together. So what did we learn? Well, if we assume the heterozygous genotype, red R, blue R, then there are three different dominance patterns that we might see for a specific trait. In complete dominance, only one allele in the genotype, the dominant allele, is seen in the phenotype. And this was the example with the red flower. In co-dominance, both alleles in the genotype are seen in the phenotype. This was the example with the flower with both red and blue petals. Finally, in incomplete dominance, a mixture of the alleles in the genotype is seen in the phenotype and this was the example with the purple flower.