Write short note on co-dominance.

Vedclass pdf generator app on play store
Vedclass iOS app on app store

Co-dominance is the phenomenon in which two alleles express themselves independently when present together in an organism.

In other words, it is the phenomenon in which offspring shows resemblance to both the parents e.g. $ABO$ blood grouping in humans.

$ABO$ blood groups are controlled by the gene $I.$

The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene.

The gene I has three alleles $I^{A}, I^{B}$ and $i .$

The alleles $\mathrm{I}^{\mathrm{A}}$ and $\mathrm{I}^{\mathrm{B}}$ produce a slightly different form of a sugar while allele 'i' does not produce any sugar.

In humans, each person possesses any two of the three I gene alleles.

$\mathrm{I}^{\mathrm{A}}$ and $\mathrm{I}^{\mathrm{B}}$ are completely dominant over i.

When $I^{B}$ and i are present only $I^{B}$ express (because 'i' does not have any sugar) same is the case with $\mathrm{I}^{\mathrm{A}}$ and $\mathrm{i}$.

But when $I^{A}$ and $I^{B}$ are present together they both express their own types of sugars, this is due to co-dominance.

Therefore, the red blood cells have both $\mathrm{A}$ and $B$ types of sugars.

$=$ Since, there are three different types of alleles there can be six different combinations.

Hence a total of six different genotypes of the human $ABO$ blood types are present as given below in the table.

Table : Table Showing the Genetic Basis of Blood Groups in Human Population

Allele from Parent $1$ Allele from Parent $2$ Genotype of offspring Blood types of offspring
$\mathrm{I}^{\mathrm{A}}$ $\mathrm{I}^{\mathrm{A}}$ $\mathrm{I}^{\mathrm{A}} \mathrm{I}^{\mathrm{A}}$ $\mathrm{A}$
$\mathrm{I}^{\mathrm{A}}$ $\mathrm{I}^{\mathrm{B}}$ $\mathrm{I}^{\mathrm{A}} \mathrm{I}^{\mathrm{B}}$ $\mathrm{AB}$
$\mathrm{I}^{\mathrm{A}}$ $\mathrm{i}$ $\mathrm{I}^{\mathrm{A}} \mathrm{i}$ $\mathrm{A}$
$\mathrm{I}^{\mathrm{B}}$ $\mathrm{I}^{\mathrm{A}}$ $\mathrm{I}^{\mathrm{A}} \mathrm{I}^{\mathrm{B}}$ $\mathrm{AB}$
$\mathrm{I}^{\mathrm{B}}$ $\mathrm{I}^{\mathrm{B}}$ $\mathrm{I}^{\mathrm{B}} \mathrm{I}^{\mathrm{B}}$ $\mathrm{B}$
$\mathrm{I}^{\mathrm{B}}$ $\mathrm{i}$ $\mathrm{I}^{\mathrm{B}} \mathrm{i}$ $\mathrm{B}$
$\mathrm{i}$ $\mathrm{i}$ $i i$ $\mathrm{O}$

 

Similar Questions

Mother and father both have blood group $‘A’$. They have two children one with blood group $‘O’$ and second one with blood group $‘A’$. They have

  • [AIIMS 2009]

In the $ABO$ system, of blood group which of the following is example of co-dominance ?

In shorthorn cattle genes for red $(r_1)$, and white $(r_2)$ coat colour occur. Crosses between red $(r_1r_2)$ and white $(r_2r_2)$ produced $(r_1r_2)$ roan. This is an example of

If two persons with $‘AB’$ blood group marry and have sufficiently large number of children, these children could be classified as $‘A’$ blood group: $‘AB’$ blood group : $‘B’$ blood group in $1 : 2 : 1$ ratio. Modern technique of protein electrophoresis reveals presence of both $‘A’$ and $‘B’$ type proteins in $‘AB’$ blood group individuals.This in an example of

  • [NEET 2013]

A person with unknown blood group under $ABO$ system, has suffered much blood loss in an accident and needs immediate blood transfusion. His one friend who has a valid certificate of his own blood type, offers for blood donation without delay. What would have been the type of blood group of the donor friend?