marker-assisted selection in wheat - ictsd

Chapter 13 – Marker-assisted selection in sheep and goats 243and genetic evaluation are provided byexternal service agents. This situation is differentfrom that in poultry and pigs and tosome extent dairy, and more similar to thatin beef cattle, in the sense that the businessunits that invest in genetic information arenot the same as those providing geneticevaluation, and EBVs are available in thepublic domain. Also, genotypic informationis an explicit part of the marketing ofgenetic material. The result is that genotypicinformation is more likely to be usedoutside the usual EBV system, with thechance of being overvalued once the investmentis made. There is a place for MASand MAI based on genetic tests for clearlydemonstrated phenotypic effects with economicbenefit, for example for disease,fecundity and meat quality.The number of detected and confirmedQTL is low for sheep and goats and genemapping is less advanced than in otherlivestock species. There is significant investmentand progress being made in markerdevelopment and gene discovery, but itwill take some years before large amountsof genetic information become available atlittle cost, e.g. in the form of SNP chips.Until then, genotypic information will provideadditional selection criteria, makingoptimal selection a greater challenge.Ultimately, the additional value of genemarkers will be greatest in breeding programmesthat already use intensive pedigreeand performance recording, and it will helpto shift selection pressure towards traitsthat are hard to improve based on phenotypic(BLUP) selection (i.e. traits suchas fertility, disease resistance and carcassquality). It is not essential that genetictests are based on functional mutations,as gene markers can have predictive valuedue to being in linkage disequilibrium withfunctional genes. In breeding programmeswithout extensive recording, it is moreimportant to rely on direct markers, butthis will only be valuable in practice ifgenes have very large economic effects.The same holds for genetic tests for distinctMendelian traits, but the overall valueof these traits in breeding programmes islimited. In less-developed breeding programmes,investments in pedigree andperformance recording will most likely bemore profitable than investments in genetechnology.Application of MAS or MAI in manysheep and goat breeding programmes indeveloping countries is not a priority, butopportunities exist, conditional on having aclearly visible phenotypic effect and a programmebased on well-defined objectivesand performance based selection.AcknowledgementsThe author would like to thank the followingcolleagues for providing informationabout breeding and MAS programmes:Richard Apps, Alex Ball, Stephen Bishop,Didier Boichard, Joanne Conington, SchalkCloete, Oswald Matika, Eduardo Manfrediand John McEwan. Information from JillMaddox, her Web site and her commentson the marker maps were very helpful, andRobert Banks made useful comments andimprovements to the manuscript.ReferencesAcin, C., Martin-Burriel, I., Monleon, E., Rodellar, C., Badiola, J. & Zaragoza, P. 2003.Characterization of the caprine PrP-gene study of new polymorphisms and relationship with theresistance/susceptibility to the scrapie disease. Proc. Internat. Workshop on Major Genes in sheepand Goats. 8–11 December 2003. CD-ROM Communication No. 2-31. Toulouse, France.