In human beings blood grouping is controlled by

Options

A. 4 alleles in which `I^(A)` is dominant
B. 3 alleles in which `I^(A) and I^(B)` are dominant
C. 2 alleles in which none is dominant
D. 3 alleles in which `I^(A)` is recessive

Answer

**Step-by-Step Text Solution:**

1. **Understanding Blood Grouping in Humans:**
- Blood grouping in humans is determined by the ABO blood group system. This system is controlled by specific alleles.

2. **Identifying the Alleles:**
- There are three main alleles involved in the ABO blood group system:
- IA (which codes for blood group A)
- IB (which codes for blood group B)
- I (which is recessive and codes for blood group O)

3. **Dominance Relationships:**
- The alleles IA and IB are co-dominant, meaning that when both are present, they will express their traits equally (resulting in blood group AB).
- The allele I is recessive, meaning that it will only express the O blood group when both alleles are I.

4. **Possible Genotypes and Blood Groups:**
- The possible genotypes and their corresponding blood groups are:
- Blood group A: Genotype can be IAIA (homozygous) or IAi (heterozygous).
- Blood group B: Genotype can be IBIB (homozygous) or IBi (heterozygous).
- Blood group AB: Genotype is IAIB (both alleles are present).
- Blood group O: Genotype is ii (both alleles are recessive).

5. **Evaluating the Options:**
- Now, let's evaluate the options provided in the question:
- **Option A:** Four alleles in which IA is dominant - Incorrect, as there are only three alleles.
- **Option B:** Three alleles in which IA and IB are dominant - Correct, as both IA and IB are co-dominant.
- **Option C:** Two alleles in which none is dominant - Incorrect, as there are three alleles and dominance exists.
- **Option D:** Three alleles in which IA is recessive - Incorrect, as IA is actually dominant.

6. **Conclusion:**
- The correct answer is **Option B:** Three alleles in which IA and IB are dominant.

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