Frank and Maria both had normal vision. After they married, they had two daughters and a son. Both daughters had normal vision and never had children. Marco, the son, was color blind. He married Lauren, who had normal vision. Marco and Lauren had two children, Caleb and Molly. Caleb was not color blind, but Molly was. Color blindness is a sex-linked trait (carried on the X chromosome). The diagram below shows the family tree.