A man whose father was colourblind marries a woman, who had a colourblind mother and normal father. What percentage of male children of this couple will be colourblind?

Options

A. 0.25
B. 0
C. 0.5
D. 0.75

Explanation

To solve the problem of determining the percentage of male children who will be colorblind from a couple where the man has a colorblind father and the woman has a colorblind mother and a normal father, we can follow these steps:

### Step 1: Determine the Genotype of the Man
The man’s father is colorblind, which means his genotype is X^cY (where X^c represents the colorblind allele). Since the father passes on his Y chromosome to his sons, the man must have inherited his normal X chromosome from his mother. Therefore, the man’s genotype is X^NY (normal vision).

**Hint:** Remember that colorblindness is a recessive trait linked to the X chromosome.

### Step 2: Determine the Genotype of the Woman
The woman has a colorblind mother (X^cX^c) and a normal father (XY). Since she inherits one X chromosome from each parent, her genotype must be X^cX (she is a carrier for colorblindness).

**Hint:** The mother’s genotype determines whether the daughter is a carrier or affected.

### Step 3: Set Up the Cross
Now we will cross the genotypes of the man (X^NY) and the woman (X^cX):
- Male: X^NY
- Female: X^cX

### Step 4: Determine Possible Offspring Genotypes
Using a Punnett square, we can determine the possible genotypes of their children:

| | X^c (from mother) | X (from mother) |
|---------|-------------------|-----------------|
| X^N (from father) | X^cX^N (carrier female) | X^NX (normal female) |
| Y (from father) | X^cY (colorblind male) | XY (normal male) |

From this, we can see the possible offspring genotypes:
- X^cX^N (carrier female)
- X^NX (normal female)
- X^cY (colorblind male)
- XY (normal male)

### Step 5: Calculate the Percentage of Male Children That Are Colorblind
From the Punnett square, we see that:
- There are 2 male offspring genotypes: X^cY (colorblind) and XY (normal).
- Out of these 2 male offspring, 1 is colorblind.

Thus, the percentage of male children that will be colorblind is:
- 1 out of 2 male children = 50%

**Final Answer:** 50% of male children will be colorblind.

---