CO DOMINANCE AND MULTIPLE ALLELES

In most cases, each gene has two distinct alleles. The dominant allele is dominant, while the recessive allele is recessive. In the heterozygous state, the dominant allele expresses its phenotypic while repressing the recessive allele, according to Mendelian inheritance. 

Some genes, on the other hand, have 3 or more alleles for a single feature. Multiple alleles are what they’re called. Furthermore, codominance is indeed a non-Mendelian ancestry. Offspring inherit both parental genes as a mixture of both genes in this event. 

As a result, both genes are equally expressed in the progeny.

CODOMINANCE MEANING:

In one phenotypic, codominance is the expression of both alleles’ effects independently. It’s a relationship between alleles of a gene that’s similar to a dominance relationship. Furthermore, it is a non-Mendelian inheritance type. 

Both alleles are completely expressed in the heterozygous condition, and each allele has its own influence on the child. In codominance, neither allele suppresses the influence of the other. 

As a result, neither the dominant nor recessive phenotype exists. Instead, it is made up of a mix of the two characteristics. Without combining the individual effects, both alleles exhibit the phenotype with its effect. When the codominance condition exists, the impacts of both alleles can be readily differentiated in the final phenotype. Furthermore, codominance has no quantitative effect.

Codominance is exemplified by the ABO blood group system. Both allele A and allele B are mutually dominant. As a result, blood type AB is neither A nor B. Because of the codominance between A and B, it functions as a separate blood group. 

The tabby cat is another great illustration of codominance. When pure black and brown cats mate, the first filial generation is made up of kitten (tabby cats) that are black with brown stripes or spots, or vice versa. Shorthorn cattle exhibit codominance as well.

MULTIPLE ALLELES:

Multiple alleles refer to traits with more than two distinct alleles. Multiple alleles, in other words, are three or more distinct alleles that code for the same trait. There are three alleles in the ABO blood group system in humans. IA, IB, and I are their names. 

A blood group, B blood group, AB blood group, and O blood group are the four phenotypes created by these three alleles. As a result, at the population level, numerous alleles may exist. These alleles may be found in different pairs in different people in the population.

EXAMPLES OF MULTIPLE ALLELES:

• COAT COLOUR OF CATS:

Domestic cats have been bred for thousands of years to produce a wide range of coat colors. The gene that controls the cat’s coat color appears to have several versions, since coat colors range from black to orange to brown to white. This indicates that the coat color is determined by several alleles.

In the population, the coat color gene has numerous alleles, as well as the pigment-producing proteins will be determined by the inheritance and expression of these alleles. Curliness, shading, patterning, and even texture is all controlled by the same genes. Because of the numerous different genotype combinations and expressions resulting from these genes, a large range of breeds exists. Even when only two parents share four alleles for each child.

Cats’ coat color phenotype — spots of black & orange (tortoiseshell patterns), black, grey, white, plus patches of white hair — strongly demonstrates multiple allelism, as there appear to be more than two alleles for the coat color phenotype (piebald spotting).

The genotype of a cat may usually be detected by looking at its coat colors and pattern. It is usually possible to forecast the color possibilities of kittens if the phenotypes of the parental cats are known, however the computations would be complex in most circumstances.

• BLOOD GROUPING IN HUMANS:

Humans and other species have qualities with three or more different types of alleles (genes). Multiple allele inheritance refers to the inheritance of three or more different alleles in a trait. The ABO blood type alleles/trait in humans is an example of a multiple allele trait. There are three types of alleles: allele A (IA), allele B (IB), and allele i. (IO or i).

Protein A is created when the allele A is present on the chromosome, and protein A is found on the membranes of the individual’s red blood cells. Protein B will be created if the allele B is present on the chromosome, and protein B will be found in the membranes of red blood cells.

Finally, neither protein A nor protein B will be generated if allele I is present on the chromosome. The ABO blood group trait is made up of these three alleles.

 COMMONALITIES BETWEEN MULTIPLE ALLELES AND CODOMINANCE:

• The ABO blood group in humans has numerous alleles and codominance.
• Mendelian inheritance does not apply to multiple alleles or codominance.

DIFFERENCE BETWEEN MULTIPLE ALLELES AND CODOMINANCE:

Codominance is a condition in which kids inherit features from both parents’ genes, regardless of whether they are dominant or recessive. Multiple alleles, on the other hand, are three or more distinct alleles that a trait carries. So, the main distinction among codominance & multiple alleles is this.

CONCLUSION:

Genes are divided into alleles, which are distinct variants of the same gene. For each gene, there are two alleles in most cases. At the population level, there may be three or more alleles for one trait. 

This is referred to as many alleles. In codominance, offspring inherit a combination of traits from both parents’ genes, regardless of dominant or recessive genes. The distinction among codominance & multiple alleles is summarized in this diagram.