Genetics of rat hypodactyly

Rat hypodactyly was originally described by Moutier et al. (1973) as an autosomal recessive trait. The determining gene Hd has been recently mapped to rat chromosome 10 and is closely linked to the D10Rat31/32, D10Rat30, and Myh3 loci (Křenová et al. 1998). In homozygous state (Hd/Hd), there is a variable reduction in the number of fingers and metacarpals — metatarsals of front and hind feet in males and females. Moreover, there is a male sterility in homozygotes whereas male heterozygotes are fertile. The light and electron microscopic examination confirmed disorder of spermatogenesis, loosening and vacuolization of seminiferous epithelium accompanied with a significantly decreased number of germ cells in testes of homozygotes.

In an intercross population (Wistar Hd×BN-Lx)F2, an independent segregation of the major genes Lx, coding for the PLS (polydactyly-luxate syndrome), and Hd — hypodactyly was found together with irregular interactions of Hd and Lx genes in double homozygotes (Hd/Hd, Lx/Lx). The variable phenotype manifestation of foot malformation in double homozygous animals indicated modifying 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 and male sterility, we started the production of two congenic strains by introgressing the Hd mutant gene onto the genetic backgrounds of the BN and SHR inbred strains.