AbstractThe waved alopecia (wal) mutation arose spontaneously in mice. Phenotypically, the wal mutation in a homozygous recessive state is manifested by a wavy coat. Over time, partial baldness develops, which leads to a thinning of the coat in mice. The molecular nature of the genetic defect in wal is still unknown; however, the coordinates of the chromosome locus in which the wal gene is located, a section of about 107 bp in length, has been determined in mouse chromosome 14. We examined the wal locus by sequencing the exons of candidate genes in which the mutation was expected, and performed genome-wide sequencing to identify the cause of the wal mutation. The sequences of exons of candidate genes located in this region did not carry changes that could lead to a change in the structure of the protein. However, outside the wal zone, a mutation in the Slc9a9 gene was found that is probably not associated with the wal phenotype. According to the literature, a mutation in the Slc9a9 gene leads to autism spectrum disorders. This is the first discovered spontaneous mutation in the Slc9a9 gene in mice.