Genetic analysis of the rat hypodactylous mutation

Autosomal recessive rat hypodactylous mutation Hd leads in homozygous condi tion to reductive changes of the digital arch of all feet. There is a varia ble preaxial reduction of the number of fingers in both sexes. Moreover, ho mozygous males are sterile. Testes of homozygous Hd/Hd and +/Hd adult rats were examined in the light and electron microscopes. Spatial organization o f stages of the spermatogenetic cycle was not confirmed in Hd/Hd testes com paring with +/Hd males. Significant decrease in the number of germ cells in seminiferous tubules of Hd/Hd testes was accompanied with loosening and va cuolization of the seminiferous epithelium. The assignment of the Hd locus to RNO10 excluded the suspected homology between rat and mouse Hd mutations . More precise mapping using microsatellite markers revealed dose linkage o f the Hd locus with the DIOMit8 marker defining Syb2 gene coding for synapt obrevin 2. A chromosomal segment of RNO10 carrying Hd and Syb genes is bein g incrossed onto BN and SHR inbred strains in order to examine the modifyin g influences of different genetic backgrounds.