Schilder's disease, which causes a progressive degeneration of the nervous system leading to death at about two years of age, behaves as a simple autosomal recessive trait. If a couple loses their first two children due to Schilder's disease, what is the chance that their third child will develop the disease? S=normal and s=Schilder's disease
I would assume that both have the recessive gene, which would make the probability 1/4, regardless of the bad luck they had with the previous two births. The fact that the parents lived to adulthood indicates that neither has two genes for the disease.