A colourblind man marries a daughter of a colourblind father. What will be the result in the next generation?

Colourblindness is an X-linked recessive disorder and follows criss-cross inheritance.
A colourblind man (XcY) and the daughter of a colourblind father (XcX) will produce the following offspring:

Possible gametes from the colourblind man (XcY): Xc and Y
Possible gametes from the daughter of a colourblind father (XcX): Xc and X

Punnett Square:

This results in:

• XcXc: Colourblind daughter (1/4 probability)
• XcX: Carrier daughter (1/4 probability)
• XcY: Colourblind son (1/4 probability)
• XY: Normal son (1/4 probability)

Hence, half of the sons will be colourblind. So, the correct answer is B.