ABO blood groups in humans are controlled by the gene I. it has three alleles-AA,IB and i. since thrre are three different alleles, six different genotypes are possible. How many phenotypes can occur ?

Options

A. Four
B. Two
C. Three
D. One

Answer

To solve the problem regarding the ABO blood groups in humans, we need to analyze the alleles and their corresponding phenotypes step by step.

### Step-by-Step Solution:

1. **Identify the Alleles**: The ABO blood group is controlled by the gene I, which has three alleles:
- \( I^A \) (A allele)
- \( I^B \) (B allele)
- \( i \) (O allele, which is recessive)

2. **Determine the Genotypes**: Since there are three alleles, we can form different combinations (genotypes). The possible genotypes are:
- \( I^A I^A \) (Blood group A)
- \( I^A i \) (Blood group A)
- \( I^B I^B \) (Blood group B)
- \( I^B i \) (Blood group B)
- \( I^A I^B \) (Blood group AB)
- \( ii \) (Blood group O)

Thus, we have a total of 6 different genotypes.

3. **Identify the Phenotypes**: Next, we need to determine the phenotypes (observable traits) corresponding to these genotypes:
- **Blood group A**:
- Genotypes: \( I^A I^A \) and \( I^A i \)
- **Blood group B**:
- Genotypes: \( I^B I^B \) and \( I^B i \)
- **Blood group AB**:
- Genotype: \( I^A I^B \)
- **Blood group O**:
- Genotype: \( ii \)

4. **Count the Unique Phenotypes**: From the analysis above, we can see that there are four unique blood groups (phenotypes):
- A
- B
- AB
- O

5. **Conclusion**: Therefore, the total number of phenotypes that can occur from the given genotypes is **4**.

### Final Answer:
The number of phenotypes that can occur is **4**.

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