Gene mapping within the T/t complex of the mouse. I. t-Lethal genes are nonallelic.

The t haplotypes of mouse chromosome 17 are natural polymorphisms in wild populations that contain mutations that affect or control such diverse functions as tail length, embryonic lethality and maturation and function of male germ cells. The major impediment to dissecting the genetics of this complex region has been its unusual property of recombination suppression in heterozygotes with wild-type chromosomes. Recently it was shown that recombination suppression does not occur in heterozygotes containing two different t haplotypes, which suggested that t chromosomes may be mismatched with respect to wild-type but share sequences that permit crossing-over between them. Thus for the first time questions of allelism and map positions of the t-lethal mutations can be addressed. We report here the results of three experiments that analyzed the tw12 haplotype trans to either tw5, tw32 or tw18. In all cases these lethal mutations were nonallelic to tw12. These results, together with evidence for functional relatedness, suggest the t-lethals may be a gene family spread out over more than 15 centiMorgans of chromosome 17.