ABO blood groups is a good example of co-dominance. Justify.

Explanation

### Step-by-Step Solution:

1. **Understanding ABO Blood Groups**: The ABO blood group system is determined by the presence of specific antigens on the surface of red blood cells. There are four main blood types: A, B, AB, and O.

2. **Role of Gene I**: The ABO blood groups are controlled by a single gene known as the gene I. This gene has three different alleles:
- IA (which produces A antigens)
- IB (which produces B antigens)
- i (which does not produce any antigens, hence is recessive).
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