From what I understand dominance to caused due to ablity of gene to produce a particular protein and recessive character is because the gene does not proteins. Whereas co-dominance is because proteins for 2 two characters are produced together. Then How does Incomplete domainance work. Please explain with respect the protein production.
- A gene has the instructions for making a specific protein. Each protein does a particular job in the cell.
- So, let’s say there is a gene involved in making a flower red. It makes a protein whose job it is to make a red pigment. This gene comes in two forms or alleles, R and r. This flower has two copies of each of its genes. So, in terms of red flower gene, the flower can be RR, Rr or rr.
- Let’s say that both RR and Rr are red and rr is white. If this is the case, then R is dominant over r because RR and Rr are the same colour. We can also say that r is recessive to R for the same reason. Now, it won’t matter if r is recessive because it makes no protein, a broken protein or a version of the protein that makes white pigment. In each case, r is recessive to R.
- Let’s say instead that RR is red, Rr is pink and rr is white. When this happens, we say that R is incompletely dominant over r. But again, the reason why being Rr leads to a pink colour doesn’t matter in terms of this being incompletely dominant.
- One way Rr might end up pink is something called haploinsufficiency. The idea here is that one R only makes enough pigment to give a pink color and so you need both to be R to get red pigment. In this case, r might make no protein or a defective one and you’d still get pink.
- Another way incomplete dominance might work is if R makes a protein that makes red pigment and r makes one that makes a white pigment. Both make a working protein but the white dilutes the red leading to pink.
- Incomplete dominance is a heterozygous genotype that creates an intermediate phenotype which is generally a mixture. In this case, only one allele (usually the normal or "wild type") of a single gene is expressed in a dosage dependent manner, which results in an intermediate phenotype.
- Generally, in incomplete dominance the wild type allele makes a functional protein and the recessive allele either makes none or it does not have the correct function. When you breed 2 incomplete dominant alleles and if you think of this in terms of an enzyme giving 100%, 50% or 0% activity or the amount of red pigment, you can then start to see how you can get pink as well as red and white.
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