1. Multiple Alleles:
* Definition: Multiple alleles refer to the presence of more than two alternative forms of a gene within a population.
* Blood Groups: The human ABO blood group system is a classic example. The gene responsible for blood type (the "ABO gene") has three common alleles:
* I^A: Produces the A antigen on red blood cells.
* I^B: Produces the B antigen on red blood cells.
* i: Does not produce any antigens on red blood cells.
2. Codominance:
* Definition: Codominance occurs when two different alleles of a gene are both expressed in a heterozygote. Neither allele is dominant over the other, and both contribute to the phenotype.
* Blood Groups: In the ABO blood group system, the I^A and I^B alleles are codominant. This means that if an individual inherits both the I^A and I^B alleles, they will express both the A and B antigens on their red blood cells, resulting in blood type AB.
Here's a table summarizing the ABO blood group system:
| Genotype | Phenotype (Blood Type) | Antigens on Red Blood Cells |
|---|---|---|
| I^A I^A or I^A i | A | A |
| I^B I^B or I^B i | B | B |
| I^A I^B | AB | A and B |
| i i | O | None |
In Summary:
* The ABO blood group system exemplifies multiple alleles because there are three different versions of the gene responsible for blood type.
* Codominance is displayed because the I^A and I^B alleles are both expressed in heterozygotes (I^A I^B), leading to the AB blood type.
Let me know if you'd like a more detailed explanation of any of these concepts!
