The Ank2TM3 mutation is present on Sb1-marked TM3 chromosomes. The lesion in Ank2TM3 is immediately proximal to the 65D breakpoint of In(3LR)sep. It likely arose spontaneously on TM3 around the time that Sb1 was introduced and has since been propagated to al Sb1-marked TM3 balancers.