Trypanosome infection (Trypanosomosis) is the most economically important disease constraint to livestock productivity in Africa (WHO 1997). It has been known for many years that certain breeds of cattle show a remarkable resistance to the effects of trypanosomosis. This phenomenon has been termed ‘trypanotolerance’ because the host tolerates the presence of the parasites, while apparently not showing the severe anaemia and production loss which are characteristic of infection in susceptible breeds. Farming of trypanotolerance livestock provides a partial solution to livestock based agriculture in tsetse-infested areas (Murray and Dexter, 1988). Trypanotolerance is a polygenic trait, and QTL detection and estimation is being undertaken in our lab. The mouse model is a powerful animal model for studying the genetics of disease resistance (Moore and Nagle, 2000). Different inbred mouse strains show dramatically difference in their response to trypanosomosis (Morrison et al., 1978), with C57BL/6J being the most resistant, while A/J and BALB/c strains are among the most susceptible. Three trypanosomosis resistance QTL designated as Tir1, Tir2 and Tir3 were mapped to chromosome 17, 5 and 1 respectively in two F2 crosses between the susceptible A/J and BALB/c strains and the resistant C57BL/6J mice (Kemp et al., 1997). Subsequently, using F6 C57BL/6 x A/J and C57BL/6 x BALB/c advanced intercross lines (AIL), Tir1 was fine mapped to a confidence interval (CI) of less than 1cM, while Tir2, and Tir3, were mapped to a larger CIs (Iraqi et al., 2000). Tir1 represents the major trypanotolerance QTL. The aim of the  project reported here is to fine map Tir2 and Tir3 in an F12 AIL fixed for the susceptible allele at the Tir1 QTL. The hypothesis is that  fixation of the Tir1 QTL might lead to stronger expression of Tir2 and Tir3, and that use of an F12 AIL will increase recombination events facilitating finer mapping of Tir2 and 3.  

J. Nganga, John P Gibson, S. Kemp, F. Iraqi

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 13, , 13.25, 2002
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