A nuclear family may have a father, a mother, children, a pointer to the father, a pointer to the mother, and a pointer to the children. The pointers are optional. Some are always required and others are used only under certain conditions. If an AF field is used a LI field must be included. Blank is read as 9.
Unknown severity is indicated by blank or zero and is read as zero.
Severity classes must be ordered by increasing severity. In the latter case if diathesis for an individual is missing, this field should be blank and not zero. Diathesis classes must be ordered by increasing susceptibility. Every pointer record must have a pointer relationship field specified in A3 format if a test locus is specified and as A2b format otherwise. Selection is complete if all children within a family are coded 0 in this field.