Maternal origin of a trisomy 7 in a spontaneous abortus.

Trisomy 7 has been determined in a spontaneous abortus by QFQ- and GTG-banding. The comparative study by photodensitometry of the polymorphism of the 7p14 band in GTG-banding, in both the abortus and its parents, has shown that in this case the origin of the trisomy is in the nondisjunction of the second maternal meiotic division. The factors that may have affected the process are analyzed.