In humans, the ABO blood type is under the control of autosomal multiple alleles.
Color blindness is a recessive X-linked trait.
Mom is type B and has normal color vision.
Dad is type O and is color-blind.
They have a son who is type O and is color-blind.
What is the probability that their next child will be a son who is type O and has normal color vision?
Enter your answer as a fraction (for example: 1/5).