Nonhomologous pairing in mice heterozygous for a T haplotype can produce recombinant chromosomes with duplications and deletions

We have investigated the structure and properties of a chromosomal product recovered from a rare recombination event between a t haplotype and a wild-type form of mouse chromosome 17. Our embryological and molecular studies indicate that this chromosome (t(wLub2)) is characterized by both a deletion and duplication of adjacent genetic material. The deletion appears to be responsible for a dominant lethal maternal effect and a recessive embryonic lethality. The duplication provides an explanation for the t(wLub2) suppression of the dominant T locus phenotype. A reanalysis of previously described results with another chromosome 17 variant called Tt(Orl) indicates a structure for this chromosome that is reciprocal to that observed for t(wLub2). We have postulated the existence of an inversion over the proximal portion of all complete t haplotypes in order to explain the generation of the partial t haplotypes t(wLub2) and Tt(Orl). This proximal inversion and the previously described distal inversion are sufficient to account for all of the recombination properties that are characteristic of complete t haplotypes. The structures determined for t(wLub2) and Tt(Orl) indicate that rare recombination can occur between nonequivalent genomic sequences within the inverted proximal t region when wild-type and t chromosomes are paired in a linear, nonhomologous configuration.