Inheritance of blood groups
Codominance
Some Different forms of the same gene. are both expressed in the same phenotype, this is called codominance.
Both codominant alleles are shown with upper case letters in genetic diagrams, but the letters used are different. For example, feather colour in hens may be white, black or speckled (it has both white feathers and black feathers).
The alleles can be shown as W for white and B for black.
There are three possible The alleles that an organism has for a particular characteristic, usually written as letters.: WW, BB and BW.
There are also three possible phenotypes: WW = white, BB = black, and BW = speckled.
Blood groups
The The basic unit of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production. controlling human ABO blood groups has three alleles, not just two:
- IA and IB are not An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself. over one another
- both are dominant over IO
This table shows the possible genotypes (alleles present) and phenotypes (blood group):
| Genotype | Phenotype |
| IA IA or IA IO | A |
| IB IB or IB IO | B |
| IA IB | AB |
| IO IO | O |
| Genotype | IA IA or IA IO |
|---|---|
| Phenotype | A |
| Genotype | IB IB or IB IO |
|---|---|
| Phenotype | B |
| Genotype | IA IB |
|---|---|
| Phenotype | AB |
| Genotype | IO IO |
|---|---|
| Phenotype | O |
So to inherit blood group A you must receive an IA allele from one parent and either an IA or an IO allele from the other. To inherit blood group B you must receive an IB allele from one parent and either an IB or an IO allele from the other. To inherit blood group AB you must receive an IA allele from one parent and an IB allele from the other. To inherit blood group O you must receive an Io from both parents.