Molecular characterization of four intra-t mouse recombinants

Recombination in the proximal region of mouse chromosome 17 is greatly reduced in heterozygotes carrying the wild-type and the t complex-type chromosomes. The reason for this is the presence of two non-overlapping inversions in the t complex. Rare crossing-over does, however, occur within the t complex of the t/+ heterozygotes. Here we characterize four such exceptional intra-t recombinants, t^Tu1 through t^Tu4. To map the positions of the genetic exchange in these four recombinants, we analyzed them with DNA probes specific for 16 loci distributed over the t complex. The analysis revealed that in three of the four recombinants, an equal crossing-over occurred in the short region between the two inversions, producing chromosomes carrying either the proximal inversion only (t^Tu1 and t^Tu4) or the distal inversion only (t^Tu2). In the fourth recombinant (t^Tu3), unequal crossing-over occurred within the proximal inversion between loci D17Leh119 and D17Leh66, producing a chromosome in which the region containing loci Tcp-1, T, and D17Tu5 has been duplicated. The duplication of the Brachyury locus leads to the suppression of the tail-shortening effect normally produced by the interaction of the dominant (T) and recessive (tct) alleles at this locus so that the T/t^Tu3 mice have normal tails.