If two persons with 'AB' blood group marry and have sufficiently large number of children, these children could be classified as 'A' blood group: 'AB' blood group 'B' blood group in 1:2:1 ration. Modern technique of protein electrophoresis reveals presence of both 'A' and 'B' type proteins in 'AB' blood group individuals. This is an example of

Options

A. Incomplete dominance
B. Particle dominance
C. Complete dominance
D. Codominance

Answer

To solve the question, we need to analyze the genetic inheritance of blood groups in humans, specifically focusing on the 'AB' blood group and the offspring produced when two individuals with this blood group reproduce.

### Step-by-Step Solution:

1. **Understanding Blood Groups**:
- Blood groups in humans are determined by the ABO blood group system, which includes three alleles: A, B, and O.
- The A and B alleles are co-dominant, meaning that if both are present in an individual, both will be expressed, resulting in the AB blood group.

2. **Gamete Formation**:
- When two individuals with AB blood group (genotype: IAIB) reproduce, each parent can produce two types of gametes: one carrying the A allele (IA) and one carrying the B allele (IB).

3. **Punnett Square Analysis**:
- To determine the possible blood groups of their children, we can set up a Punnett square:
```
IA IB
----------------
IA | IAIA (A) | IAIB (AB) |
----------------
IB | IAIB (AB) | IBIB (B) |
----------------
```
- The resulting genotypes from this cross are:
- 1 IAIA (A blood group)
- 2 IAIB (AB blood group)
- 1 IBIB (B blood group)

4. **Ratio of Blood Groups**:
- From the Punnett square, we can see that the ratio of the blood groups among the offspring is 1:2:1 (A:AB:B).

5. **Electrophoresis and Co-dominance**:
- The question mentions that modern techniques like protein electrophoresis reveal the presence of both A and B type proteins in individuals with AB blood group.
- This observation indicates that both alleles (A and B) are expressed simultaneously in the phenotype, which is a characteristic of co-dominance.

6. **Conclusion**:
- Therefore, the inheritance pattern described in the question, where both A and B proteins are present in AB blood group individuals, exemplifies co-dominance.

### Final Answer:
The answer is **co-dominance**.