Humans inherit colour of their eyes from their parents. Brown-eyed couple has three blue-eyed children. Which of the following statements gives correct explanation of this situation?
(i) Each parent has an allele for brown eyes and an allele for blue eyes.
(ii) The allele for blue eyes is recessive.
(iii) The probability that their next child will have blue eyes is 75%.
(iv) The probability that their next child will have brown eyes is 50%.

Options

A. (i) and (ii) only
B. (i) and (iii) only
C. (ii) and (iv) only
D. (iii) and (iv) only

Answer

To solve the question about the inheritance of eye color in a brown-eyed couple with blue-eyed children, we can break it down step by step:

### Step-by-Step Solution:

1. **Understanding Eye Color Genetics**:
- Eye color is determined by alleles, which are different forms of a gene. In this case, we denote brown eyes with the allele "B" (dominant) and blue eyes with the allele "b" (recessive).

2. **Parental Genotypes**:
- Since both parents have brown eyes but have blue-eyed children, it indicates that both parents must carry one allele for brown eyes (B) and one for blue eyes (b). Thus, their genotypes are heterozygous: Bb (for both parents).

3. **Punnett Square Analysis**:
- To understand the possible combinations of alleles in their children, we can use a Punnett square:
```
B b
----------------
B | BB | Bb |
----------------
b | Bb | bb |
----------------
```
- The combinations show:
- BB: Brown eyes (25%)
- Bb: Brown eyes (50%)
- bb: Blue eyes (25%)

4. **Interpreting the Results**:
- From the Punnett square, we can see that there is a 25% chance for each child to have blue eyes (bb) and a 75% chance for them to have brown eyes (BB or Bb).

5. **Evaluating the Statements**:
- (i) Each parent has an allele for brown eyes and an allele for blue eyes. **(True)**
- (ii) The allele for blue eyes is recessive. **(True)**
- (iii) The probability that their next child will have blue eyes is 75%. **(False, it is 25%)**
- (iv) The probability that their next child will have brown eyes is 50%. **(False, it is 75%)**

6. **Conclusion**:
- The correct statements that explain the situation are (i) and (ii).