A normal-visioned man whose father was colour-blind, marries a woman whose father was also colour-blind. They have their first child as a daughter. What are the chances that this child would be colour-blind?

Options

A. zero percent
B. 0.25
C. 0.5
D. 1

Answer

To solve the problem regarding the chances of the daughter being color-blind, we need to analyze the genetic information provided. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Genetic Background
Color blindness is a sex-linked recessive trait, which means the gene responsible for color blindness is located 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 Man
The man in the question has normal vision but his father was color-blind. Since color blindness is recessive, the man must have inherited one normal vision X chromosome from his mother and a Y chromosome from his father. Therefore, his genotype is:
- X^H Y (where X^H represents the normal vision allele).

### Step 3: Determine the Genotype of the Woman
The woman has a father who was color-blind, which means she must have inherited the color-blind allele from him. Since she is not stated to be color-blind herself, she must be a carrier. Thus, her genotype is:
- X^H X^h (where X^H represents the normal vision allele and X^h represents the color-blind allele).

### Step 4: Set Up the Punnett Square
To find the possible genotypes of their offspring, we can set up a Punnett square:

| | X^H (from man) | Y (from man) |
|---------|-----------------|---------------|
| X^H (from woman) | X^H X^H | X^H Y |
| X^h (from woman) | X^H X^h | X^h Y |

### Step 5: Analyze the Offspring
From the Punnett square, we can see the possible genotypes for their children:
1. X^H X^H (normal vision female)
2. X^H X^h (carrier female)
3. X^H Y (normal vision male)
4. X^h Y (color-blind male)

### Step 6: Focus on the Daughter
Since the question specifies that they have a daughter, we only consider the female offspring:
- The possible genotypes for daughters are X^H X^H (normal vision) and X^H X^h (carrier).
- Neither of these genotypes results in color blindness.

### Conclusion
The chances that the daughter would be color-blind are 0%.

### Final Answer
**0%**

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