Colour blindness is a recessive trait. A couple with normal vision has two sons - one colourblind and one with normal vision. If the couple has two daughters, what proportion of them will have normal vision?

Explanation

To solve the question about the inheritance of color blindness in a couple with normal vision who have two sons (one colorblind and one with normal vision) and two daughters, we can follow these steps:

### Step 1: Understand the Genetics of Color Blindness
Color blindness is an X-linked recessive trait. This means that the gene responsible for color blindness is located on the X chromosome, and a person needs two copies of the mutated gene (in females) or one copy (in males) to express the trait.

### Step 2: Determine the Genotypes of the Parents
Since the couple has normal vision, we can denote their genotypes:
- The father must have the genotype **XY** (normal vision).
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