First comprehensive low-density horse linkage map based on two 3-generation, full-sibling, cross-bred horse reference families

Two 3-generation full-sibling reference families have been produced and for m a unique resource for genetic linkage mapping studies in the horse. The F -2 generations, now comprising 61 individuals, consist of 28- to 32-day-old embryos removed nonsurgically from two pairs of identical twin mares. The same stallion shed all F(2)s such that the two full-sibling families are ha lf-sibling with respect to each other. The families are crossbred to maximi ze levels of heterozygosity and include Arabian, Thoroughbred, Welsh Cob, a nd Icelandic Horse breeds. Milligram quantities of DNA have been isolated f rom each embryo and from blood samples of the parents and grandparents. The families have been genotyped with 353 equine microsatellites and 6 biallel ic markers, and 42 Linkage groups were formed. In addition, the physical lo cation of 85 of the markers is known, and this has allowed 37 linkage group s to be anchored to the physical map. The inclusion of dams in the genotypi ng analysis has allowed the generation of a genetic map of the X chromosome . Markers have been assigned to all 31 autosomes and the X chromosome. The average interval between markers on the map is 10.5 cM, and the linkage gro ups collectively span 1780 cM. The results demonstrate the benefits for hor se Linkage mapping studies of genotyping on these unique full-sibling famil ies, which comprise relatively few individuals, by the generation of a comp rehensive low-density map of the horse genome. (C) 2000 Academic Press.