Horse Geneticists Meet in Brisbane, Australia Horse geneticists met July 4-6, 2001 in Brisbane, Australia for the Fourth International Equine Gene Mapping Workshop. Forty-two scientists from Europe, Asia, Australia and America met to present their research and discuss collaborative efforts to build the map at the meeting organized by Dr. Kevin Bell of the University of Queensland. This series of workshops began in 1995 under the auspices of the Dorothy Russell Havemeyer Foundation with the goal of creating a powerful new research tool to benefit of the health and welfare of horses. This effort is similar to the human genome program. However, unlike the human project designed to completely sequence the human genome, the horse mapping effort is directed at the simpler task of identifying landmarks on chromosomes and creating a framework for studying horse genes. Nevertheless, the human gene sequences have been valuable for horse research because the organization of the horse genome has proven to be very similar to that of the human genome. Indeed, many horse genes show 90%-95% conservation with human sequence and large chromosome segments appear the same in both species. Therefore, scientists can use the human map to predict the structure and organization of the horse genome. Progress was readily apparent since the 1999 workshop meeting in Uppsala, Sweden. In Sweden, only 485 DNA markers and genes were mapped to chromosomes. In Brisbane, that number almost reached 1000, doubling the density of the map in just two years. Scientists also reported preliminary studies applying the gene map to identify inherited aspects of diseases including muscle diseases, bone disorders, epitheliogenesis imperfecta, megacolon disease, cerebellar hypoplasia as well as genes controlling coat colors in horses. Future work will focus on increasing the density of markers, determining their order on chromosomes, comparative mapping to better determine the correlation between the human and horse gene maps and applying the information to investigate and understand the genetics of the horse. Specific Summary: A central activity for the workshop has been development of a linear linkage map for the horse using primarily microsatellite DNA markers but also other types of polymorphic markers. Gerard Guerin presented information about the current status of the workshop half sibling family, based on 13 sires and 480 offspring. DNA from this family is available to all scientists for linkage mapping; the family is large and diverse providing many opportunities to identify linkage relationships between genetic markers. The current dataset was produced using data from 20 laboratories in addition to the previously published data (Guerin et al., 1999). Guerin reported his analysis for the results from testing 327 markers on the pedigrees and constructed a linear map using CRIMAP. 281 of the 327 markers were placed on the linkage map based on a lod score of 3.0 or greater. Every chromosome included a linkage group and the span of the linkage map was 2126 cM. Considerable use of the Newmarket full sibling family has been made for selection of markers to place on this linkage map. Markers were selected based on their potential to contribute to gaps in the half-sibling linkage map, as well as markers not informative on the full-sibling map. Work continues to expand this map in connection and in support of development of the radiation hybrid map. June Swinburne discussed advances with the Newmarket map. This is a full sibling map based on a stallion bred to two sets of identical twins to produce 60 offspring. This family provides a powerful means to study linkage since both male and female meioses can be used. Furthermore, this family makes it possible to make a linkage map including the X-chromosome as well as using di-allelic markers.