There are two types of blindness in humans, each defined by its own recessive autosomal gene. The genes for both traits are on different

There are two types of blindness in humans, each defined by its own recessive autosomal gene. The genes for both traits are on different pairs of chromosomes. What is the probability of having a blind child if:
1) the father and mother suffer from the same type of hereditary blindness, and for the other pair of blindness genes they are normal and homozygous;
2) the father and mother suffer from different types of blindness, and for the other pair of blindness genes they are normal and homozygous;
3) both parents are diheterozygous;
4) parents are sighted, both grandmothers suffer from the same type of hereditary blindness, and they are normal and homozygous for the other pair of genes; from the side of grandfathers hereditary blindness in their pedigree is not noted?

The probability of having a blind child: 1) 100%; 2) 0%; 3) 43.75%; 4) 25%.