Question

If a woman with colour blindness marries a man with normal vision, the expected vision in their daughters is:

• A. Normal vision - homozygous
• B. Colour blind
• C. Normal vision - carrier
• D. Total blindness

Hint:

A colour blind mother and normal father produce all carrier daughters and all colour blind sons.

Answer 1

The Correct Option is C

Concept: Colour blindness is an X-linked recessive disorder. Let \[ X^C=\text{normal vision allele} \] \[ X^c=\text{colour blindness allele} \] A female is colour blind only when she possesses two recessive alleles. \[ X^cX^c \]

Step 1: Write the parental genotypes. Colour blind woman: \[ X^cX^c \] Normal man: \[ X^CY \]

Step 2: Determine the gametes produced. Female produces: \[ X^c \] Male produces: \[ X^C,\ Y \]

Step 3: Construct the offspring genotypes. Daughters receive: \[ X^C \text{ from father} \] and \[ X^c \text{ from mother} \] Therefore all daughters are \[ X^CX^c \]

Step 4: Interpret the phenotype. Since the dominant normal allele is present, \[ X^CX^c \] shows normal vision. However, the recessive allele is also present. Hence daughters are carriers. \[ \boxed{\text{Normal vision - carrier}} \]