Msx1 is close but not allelic to either Hm or Hx on mouse chromosome 5

The Msx1 homeobox locus has been mapped in relation to the mutations hammer-toe (Hm) and hemimelic extra toes (Hx). Msx1 is expressed in the developing limb, while limb development is affected by the Hm and Hx mutations. Hm and Hx are very tightly linked loci. In interspecific crosses, the segregation of either mutation was followed in relation to polymorphic alleles of Msx1, Il6, and En2, to give a fine map around the mutant loci. Our results show that Msx1 is not allelic to either of the mutations, but is located about 3 cM from them. Il6 did not recombine with either Hm or Hx and, therefore, provides a point of access for the analysis of these mutations at the molecular level.