A brown eyed couple has a blue- eyed child . The trait of brown eye (B) is dominant over blue-eye (b). What is the genotype of the couple ?

Options

A. Bb `xx`Bb
B. `BB xxBB`
C. `BBxxBb`
D. `BBxxbb`

Answer

To determine the genotype of the brown-eyed couple who has a blue-eyed child, we can follow these steps:

### Step 1: Understand the Traits
- Brown eyes (B) are dominant over blue eyes (b).
- This means that a person with at least one dominant allele (B) will have brown eyes, while a person with two recessive alleles (bb) will have blue eyes.

### Step 2: Analyze the Child's Genotype
- The child has blue eyes, which indicates that the child must have the genotype (bb). This is because blue eyes are only expressed when both alleles are recessive.

### Step 3: Determine the Possible Genotypes of the Parents
- Since both parents are brown-eyed, their genotypes could either be homozygous dominant (BB) or heterozygous (Bb).
- However, if both parents were homozygous dominant (BB), they could only produce offspring with brown eyes (BB or Bb), and would not be able to produce a blue-eyed child (bb).

### Step 4: Conclusion about the Parents' Genotype
- Therefore, both parents must be heterozygous (Bb) in order to have a child with the blue-eyed genotype (bb).
- The possible combinations from two Bb parents would be:
- BB (brown eyes)
- Bb (brown eyes)
- Bb (brown eyes)
- bb (blue eyes)

### Final Answer
- The genotype of the brown-eyed couple is Bb (heterozygous).