a^18H

This mutation comprises a paracentric inversion with deletions of 20 and 18 bp from the proximal and distal breakpoints, respectively. A probe from the agouti locus that differentiates polymorphisms between C3H/HeH and 101/H was used to show that the mutation arose on C3H/HeH. The mutating event affected the regulation of agouti, down regulating the expression of pheomelanin. The distal breakpoint is in the intron between exons 1 and 2 of the Itch gene and is responsible for an immunological defect. (J:24934, J:45910)