Incomplete Dominance and Codominance

[Yuqing]

I need some help on what exactly is happening here at the cellular level.

I understand that incomplete dominance is a blending, for example caused by a functional enzyme producing pigments and a non-functioning enzyme. The result would be less pigments, therefore an apparent mixing.

But what is happening with co-dominance? You have checkered chickens and roan cows. How exactly is this caused at a cellular level? If both phenotypes are active simultaneously, shouldn't there be a uniform blending instead of having patches of colour or similar phenomena?

 

[phi29]

I'm not quite sure of the physiology of coat colors, but consider blood type. The alleles are equally expressed on the surface of RBCs, they cannot physically blend.
Your patching question makes me think of Barr body inactivation, so that only X chromosome is activated in each cell and an almost chimerism can be seen, in that some only paternal X-chrom genes are expressed in a given cell, and maternal genes in another.
Hope this helped a little bit, genetics can be confusing since there are so many mechanisms that accomplish the same effect, especially in intro courses where molecular things aren't explained.

 

[quicknote]

At the cellular level, incomplete dominance and codominance are both examples of genetic interactions between alleles. In incomplete dominance, one allele is not completely dominant over the other, resulting in a blending of traits. This occurs because the proteins produced by the two alleles have slightly different functions, and when both are present, they work together to produce a phenotype that is a combination of the two.

In codominance, both alleles are equally expressed and contribute to the phenotype. This means that both proteins are produced and have distinct functions, resulting in a phenotype that displays both traits simultaneously. This can manifest as patches of different colors or patterns, as seen in checkered chickens and roan cows.

At the cellular level, this is caused by the presence of two different alleles of the same gene. Each allele produces a slightly different protein, and when both are present, they work together to produce a unique phenotype. This can be seen in the case of checkered chickens, where one allele produces black feathers and the other produces white feathers. When both are present, the result is a checkered pattern.

In the case of roan cows, the codominant alleles produce different types of red pigment. When both are present, the result is a mixture of red and white hairs, giving the cow a roan appearance.

Overall, incomplete dominance and codominance demonstrate the complex interactions between alleles at the cellular level, resulting in a variety of phenotypes that are not always easily predicted. These genetic interactions are important to understand in order to fully grasp the complexity of inheritance and evolution.