The ABO blood group is determined by three alleles. Heterozygotes I^A I^B express both A and B antigens on red blood cells.
Why is the AB phenotype an example of both codominance and multiple alleles?
- A
I^A and I^B are X-linked alleles producing the AB phenotype.
- B
Only one allele is expressed; the gene has only two alleles.
- C
The heterozygote shows an intermediate blood type.
- Dcheck_circle
Both I^A and I^B are expressed simultaneously, and three alleles (I^A, I^B, i) exist for the gene.
Explanation
The ABO gene has three possible alleles (multiple alleles). In an I^A I^B heterozygote, both A and B antigens are produced, illustrating codominance.