Gene mapping within the T/t complex of the mouse. III: t-Lethal genes are arranged in three clusters on chromosome 17.

Lethal t mutations belonging to seven different complementation groups have been mapped. The overall picture emerges as three clusters of t-lethal genes: one near the proximally located tail interaction factor (tT) containing tw73; one numerous cluster associated with the MHC and including tw32, t12, tw5, tw18, and tLub-1; and one distal cluster close to the locus of tf encompassing, t0, t6, and tw12. In the two cases examined, members of the same complementation group map to the same location. Evidence is presented that more than one mutant site may be necessary for the lethality of some lethal t "mutations," and that the expression of a specific lethal phenotype may depend on cis-interactions between multiple mutations.