This duplication on Chromosome 4 was identified among the offspring of a (C3H/HeH x 101H)F1 male mouse that received triethylenemelamine and 3-aminobenzamide plus 6 Gy X-rays and later was mated to a tester (PT) female. Cytogenetic analysis suggests it is most likely an inverted duplication of bands 4A3-B1. (J:192799)