A pair of mutant mice with a first sparse coat appeared spontaneously in the production stock of BALB/c mice with a normal coat. After being sib-mated, they produced three phenotypes in their progeny: mice with normal hair, mice with a first sparse coat and then a fuzzy coat, and uncovered mice. Genetic studies revealed the mutants had inherited an autosomal monogene that was semi-dominant. By using 11 biochemical loci – Idh, Car2, Mup1, Pgm1, Hbb, Es1, Es10, Gdc, Ce2, Mod1 and Es3 – as genetic markers, two-point linkage tests were made. The results showed the gene was assigned to chromosome 11. The result of a three-point test with Es3 and D11Mit8 (microsatellite DNA) as markers showed that the mutation was linked to Es3 with the recombination fraction 7·89±2·19%, and linked to D11Mit8 with the recombination fraction 26·30±3·57%. The recombination fraction between Es3 and D11Mit8 was 32·90±3·81%. It is suggested that the mutation is a new genetic locus that affected the skin and hair structure of the mouse. The mutation was named uncovered, with the symbol Uncv. Further studies showed the mutation affected not only the histology of skin and hair but also the growth and reproductive performance of the mice. The molecular characterization of the Uncv locus needs to be further studied.