NONHOMOLOGOUS PAIRING IN MICE HETEROZYGOUS FOR A t HAPLOTYPE CAN PRODUCE RECOMBINANT CHROMOSOMES WITH DUPLICATIONS AND DELETIONS

Nora Sarvetnick ¹, Howard S. Fox ¹, Elizabeth Mann ², Paul E. Mains ¹, Rosemary W. Elliott ², and Lee M. Silver ³

¹ Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724
² Department of Molecular Biology, Roswell Park Memorial Institute, Buffalo New York 14263
³ Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544

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.

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