Jenna and Isaac meet at college. They have many interests in common, including the fact that they were both adopted. They fall in love and get married.
As they later discover their biological family histories, they are shocked to find out that they have a grandparent in common, and they are even further disturbed to find out this common ancestor was a carrier of a rare, recessively inherited disorder.
There are no genetic tests available for the recessive disorder allele that Isaac and Jenna may carry.
Based on the available information, what is the probability that a child of Isaac and Jenna would be afflicted with this disorder?