A new set of recombinant inbred strains complementary to HXB and BXH sets

Summary A new set of recombinant inbred [RI]strains has been developed complementary to the original RI strains BXH/HXB using the BXH2 RI strain and the SHR- Lx congenic strain as progenitors, both homozygous in Lx locus. The reason behind the production of this lies in a special SHR/BN gene combination in the BXH2 strain which is increasing the expressivity of the Lx gene and sensitizes this strain to teratogenic effects. On the contrary, the SHR genetic background minimizes the Lx gene expression as well as the teratogenic action of retinoic acid. There are 10 PXO strains in 17 th up to 21 st generation of inbreeding. The variability of leg malformation on PXO strains is similar to that in BXH/HXB polydactylous RI strains. The genotyping of PXO RI set has been started showing relatively high degree of homozygosity [over 90%] in individual RI strains. After inbreeding is accomplished the PXO will have become a useful complement to the original RI strain system. In preliminary teratologic testing, variable sensitivity to retinoic acid has been shown in 3 PXO strains.