In genetics , dominance belongs to the property that a gene (or allele ) has in relation to other genes or alleles. A gene or allele shows dominance when it suppresses the expression, or dominates the effects, of the recessive gene or allele . There are different forms of dominance such as complete dominance, incomplete dominance and codominance . Codominance is a form of dominance in which the alleles of a pair of genes in a heterozygote are fully expressed. This results in offspring with a phenotype that is neither dominant norrecessive . It is a non-Mendelian hereditary model in which the recessive gene does not exist, but, on the contrary, both genes behave as dominant . Codominance is represented by a capital letter.


What is codominance?

Codominance is the situation that arises when two of the alleles that are different are found in the genotype and both manage to be expressed, producing a phenotype with characteristics of both.

  • What is understood by codominance and incomplete dominance
  • Difference between intermediate inheritance and codominance
  • Examples of codominance

What is understood by codominance and incomplete dominance

To understand the term and the difference, it is important to first refer to where the term codominance came from. The Mendel ‘s laws of inheritance emerged from investigations crosses between plants made by Gregor Mendel, an Austrian Augustinian monk, in the nineteenth century. Between 1856 and 1863, Gregor Mendel grew and tested about 28,000 pea plants. His experiments led him to conceive two generalizations that would later be known as Mendel’s Laws of inheritance or Mendelian inheritance . The conclusions are described in his article entitled “Experiments on plant hybridization “ which was read to the History SocietyNatural on February 8 and March 8, 1865 and then it was published in 1866 and from here comes the term codominance.


Codominance is different from incomplete dominance in that the former has both alleles that manifest the phenotypes while the latter produces an intermediate phenotype . The codominance genes of heterozygous organisms are equivalent to that of their peers. Heterozygotes have two alleles of a gene in common in relation to the trait . Codominance is also said to be a state in which genes can give rise to a phenotype with the same characteristics. In the case of incomplete dominance , the alleles are expressed, but in a genotype they have intermediate characteristics. In this type of dominance, heterozygotes have two alleles that can be expressed but cannot be joined . Codominance is the process by which a species can manifest two dominant characteristics in its phenotype, while incomplete dominance is the genetic interaction in which homozygotes are phenotypically different from heterozygotes. The crosses that have incomplete dominance are those in which there is no dominant or recessive trait.

Difference between intermediate inheritance and codominance

The hybrid manifest the phenotype corresponding to only one of the alleles possess. When a character , for example, such as the color of peas, behaves in this way it is said to follow a dominant inheritance pattern . But there are other characters that are not inherited in the same way. For example, the color of the flower petals of some plants: hybrids of the crossing of two pure races of white flowers (rr) and red flowers (RR) have an Rr genotype and an intermediate phenotype between those of their parents, is say pink. This mode of inheritance is called intermediate and the two alleles are said to be equipotent.. The intermediate inheritance then provides us with a phenotype in between, between one extreme and another, for example, applied to human beings. In this regard, it is also important to remember that inheritance requires genes and that they are found along the chromosomes, so those that are in the same tend to be inherited at the same time.

Examples of codominance

A typical example showing a codominance is the ABO blood group system . For example, a person who has an A allele and a B allele will have an AB blood type because both alleles A and B are codominant with each other. An example of an allele or a gene is colored a flower . A flower can have alleles that make it red or pink, and so on. Alleles that always appear when present are known as dominant alleles. The alleles that are hidden by the dominant alleles are known as recessive alleles . In some situations, both alleles are expressed equally. A genetic scenario where neither allele is dominant or recessive and both are expressed is known ascodominance . Another fairly simple example is when a brown cow is crossed with a white bull, and offspring or calves with brown and white spots are obtained.

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