Step 1: Understand dominance patterns.
- Complete dominance: Only one allele is expressed.
- Incomplete dominance: The heterozygote exhibits an intermediate phenotype.
- Co-dominance: Both alleles in a heterozygote are expressed equally and independently.
Step 2: Apply to AB blood group.
- The ABO blood group is governed by the I gene with three alleles: I\textsuperscript{A}, I\textsuperscript{B}, and i.
- Individuals with genotype I\textsuperscript{A}I\textsuperscript{B} display both A and B antigens on their red blood cells.
- Consequently, both alleles (I\textsuperscript{A} and I\textsuperscript{B}) are expressed equally without blending.
Step 3: Conclude.
The AB blood group is thus a prime illustration of co-dominance.
Final Answer: \[\boxed{\text{AB blood group shows Co-dominance.}}\]