Genetics of rat hypodactyly

Rat hypodactyly was originally described by MOUTIER et al. (1973) as an aut osomal recessive trait. The determining gene Hd has been recently mapped to rat chromosome 10 and is closely linked to the D10Rnt31/32, D10Rat30, and Myh3 loci (KRENOVA et al. 1998). In homozygous state (Hd/Hd), there is a va riable reduction in the number of fingers and metacarpals - metatarsals of front and hind feet in males and females. Moreover, there is a male sterili ty in homozygotes whereas male heterozygotes are fertile. The light and ele ctron microscopic examination confirmed disorder of spermatogenesis, loosen ing and vacuolization of seminiferous epithelium accompanied with a signifi cantly decreased number of germ cells in testes of homozygotes. In an intercross population (Wistar HdxBN-Lx)F2, an independent segregation of the major genes Lx, coding for the PLS (polydactyly-luxate syndrome), a nd Hd - hypodactyly was found together with irregular interactions of Hd an d Lx genes in double homozygotes (Hd/Hd, Lx/Lx). The variable phenotype man ifestation of foot malformation in double homozygous animals indicated modi fying influences of genes of the genetic background. In order to study more precisely the role of the determining major gene Hd as well as the role of the putative modifying genes in the development of the foot malformation a nd male sterility, we started the production of two congenic strains by int rogressing the Hd mutant gene onto the genetic backgrounds of the BN and SH R inbred strains.