A man with colour blindness has a daughter of normal phenotype. She marries a man who is not colour blind. If the married couple had four sons, what is the possibility that all four will be colour blind?

A man with colour blindness has a daughter of normal phenotype. She marries a man who is not colour blind. If the married couple had four sons, every child birth 1/2 chance is present for male to become colour blind because she is a carrier. So for four children ½ x ½ x ½ x ½ = 1/16.