GENETIC AND PHYSICAL MAPPING OF THE FITNESS-1 (FIT1) LOCUS WITHIN THEFES-HBB REGION OF MOUSE CHROMOSOME-7

Mutations at the fit1 locus affect normal pre- and post-natal developm ent by retarding growth and reducing viability. We report mapping of t he fit1 locus, by trans-complementation crosses to mice carrying delet ions of the albino (c) locus in Chromosome (Chr) 7, to a subregion of the c-deletion complex within the Mod2-shl interval. The fit1 locus, w hich is currently defined by five N-ethyl-N-nitrosourea (ENU)-induced mutations, was found to map in a subregion between the eed and exed lo ci. A restriction fragment containing a deletion breakpoint that genet ically defines the proximal border of fit1 was cloned, providing a DNA probe (RN302) that maps proximal to fit1. Long-range mapping with thi s probe, and with a DNA probe that maps distal to the fit1 interval, e stablished that the region containing at least part of the fit1 gene i s 530 kb or less. Positioning of fit1 between deletion breakpoints, an d the isolation and mapping of a DNA probe proximal to it, should faci litate the cloning and molecular characterization of fit1, as well as of the eed locus and the tightly linked l(7)5Rn and l(7)6Rn loci.