A large inverted duplication allows homologous recombination between chromosomes heterozygous for the proximal t complex inversion.

We have examined the molecular organization of a region of mouse chromosome 17 that allows homologous recombination between wild-type and t haplotype chromosomes across a large inversion. We have used a combination of genetic mapping of restriction fragment length polymorphisms, molecular characterization of cloned regions isolated on overlapping cosmids, and subchromosomal restriction mapping using the pulsed field gel technique. Our analyses show that the wild-type form of chromosome 17 contains an inverted duplication of an element of at least 650 kb that is present in only one copy in the t haplotype form. Two chromosomes, th45 and tAE5, arose by homologous recombination across the element that is present in both chromosomal variants in the same orientation.