The rat shorn mutation (shn) maps between D7Got143 and D7Rat94

The recessive shorn (shn) mutation in the rat generates an almost complete absence of normal hair. Previous analysis of 85 backcross rats typed for shn-generated hypotrichosis located this marker between the telomere and D7Mgh1 on distal rat Chromosome 7. Here, we present a microsatellite polymorphism analysis of a 184-member backcross panel-including 99 new rats-that places shn within a 2.7cM interval between markers D7Got143 and D7Rat94. In addition, this analysis has allowed meiotic ordering of 18 microsatellite markers-including 10 D7Got markers previously positioned only by radiation reduced hybrid analysis-across the 16.8cM region between D7Mit16 (Cyp2d4) and D7Rat94. Our inability to meiotically separate shn from 8 microsatellite markers (mapped by others over some 2-4cM or more than 40cR of genetic distance) suggests that the shn mutation may result from a chromosomal rearrangement that suppresses recombination throughout this interval.