Girl normal vision whose father was colourblind and marries a man of normal vision whose father was also colour blind. The sons of this marriage would be

Options

A. All normal
B. All colour blind
C. 50% colour blind
D. 25% colour blind

Answer

To solve the problem, we will analyze the genetic inheritance of colorblindness in the given scenario. Here’s a step-by-step breakdown:

### Step 1: Understand the Genetic Background
- Colorblindness is a sex-linked recessive trait carried on the X chromosome.
- Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

### Step 2: Determine the Genotype of the Girl
- The girl has normal vision, but her father is colorblind.
- Since her father is colorblind (XcY), he must have passed his X chromosome with the colorblind allele (Xc) to her.
- Therefore, the girl must have one normal vision allele from her mother (X) and one colorblind allele from her father (Xc).
- Her genotype is XcX (normal vision carrier).

### Step 3: Determine the Genotype of the Man
- The man has normal vision, and his father is colorblind.
- Since the father is colorblind (XcY), he must have passed his Y chromosome to his son.
- Therefore, the man must have received a normal vision allele from his mother (X) and has a Y chromosome from his father.
- His genotype is XY (normal vision).

### Step 4: Set Up the Punnett Square
- The girl (XcX) can contribute either Xc or X to the offspring.
- The man (XY) can contribute either X or Y to the offspring.

| | X | Y |
|---------|-------|-------|
| **Xc** | XcX | XcY |
| **X** | XX | XY |

### Step 5: Analyze the Offspring
- The possible genotypes of the offspring are:
- XcX (female, carrier of colorblindness)
- XX (female, normal vision)
- XcY (male, colorblind)
- XY (male, normal vision)

### Step 6: Determine the Sons
- The sons from this marriage can be:
- XcY (colorblind)
- XY (normal vision)

### Conclusion
- Therefore, the sons of this marriage would have a 50% chance of being colorblind and a 50% chance of having normal vision.

### Final Answer
The sons of this marriage would be 50% colorblind and 50% with normal vision.

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