The great-great maternal grandmother of a boy was a carrier for color blindness, an X-linked disorder. His great The great-great maternal grandmother of a boy was a carrier for color blindness, an X-linked disorder. His great uncle on his mother’s side was color blond but his great uncle’s father was unaffected. The boy’s mother has 2

brothers (1 color blind, 1 unaffected) and 1 sister (unaffected). The boy’s grandmother on his mother’s side had 1

brother who was color blind and 3 sisters. Two of these sisters were unaffected and one was a carrier. The boy's

great grandmother on his mother's side had 4 sisters. The boy has one unaffected sister and he is color blind.

What is the probability of the boy's sons being color blind if he marries a non-carrier?