The flailer mutation, originally called tb^2J, was a presumed remutation of tb because of a similar phenotype. This mutation, however, does not map to Chr 1, and the original unpublished report of linkage of tb to Chr 1 is in doubt. Thus, it is not clear whether tb^2J is a remutation at the tb locus which was not on Chr 1, or if tb^2J is a new mutation at a different locus. Because of its linkage to a different chromosome, tb^2J was renamed flr.

flr mutants have a variable neurological phenotype. Half of all flailer homozygotes show severe ataxia and only live for 3 weeks; these mutants tend to fall over and flail their limbs in an effort to right themselves. The other half of flailer homozygotes, however, only develop a transient ataxia; they recover, are fertile, and have a normal life span.