Genetic history, pedigree construction and inheritance patterns — branching viva

Outpatient setting: a three-year-old boy with global developmental delay whose parents are first cousins and who has a maternal uncle who died in infancy. The examiner asks: how do you construct the pedigree, what does the shape tell you about the inheritance pattern, and what is the recurrence risk — then branches to the same family producing a 15q11-q13 deletion in the next child, then to an isolated male with Duchenne muscular dystrophy and the question of germline mosaicism.