Practice question

A de novo mutation observed in a child but absent in somatic tissues of both parents most likely arises during gametogenesis. Paternal germline exhibits higher number of mitotic divisions and accumulates replication errors with advancing age, especially point mutations. Such germline mosaicism produces gametes carrying mutation not detectable in parental blood DNA. Post-zygotic origin would produce somatic mosaicism in child, maternal origin less frequent for certain autosomal dominant mutations. Laboratory artifact is excluded by validation. Hence new mutation likely originated in father's germline lineage.