marker-assisted selection in wheat - ictsd

220Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishcurrent status of MAS in dairycattleTwo ongoing MAS programmes in dairycattle have been reported to date, inFrench and German Holsteins (Boichardet al., 2002, 2006; Bennewitz et al., 2004b).Currently in the German programme,markers on three chromosomes are used.The MA-BLUP evaluations (Fernandoand Grossman, 1989) are computed at theVIT-computing centre in Verden, and aredistributed to Holstein breeders who canuse these evaluations for selection of bulldams and preselection of sires for progenytesting. The MA-BLUP algorithm onlyincludes equations for bulls and bull dams,and the dependent variable is the bull’sDYD (Bennewitz et al., 2003b). Linkageequilibrium throughout the population isassumed. To close the gap between thegrandsire families analysed in the Germangranddaughter design and the current generationof bulls, 3 600 bulls were genotypedin 2002. As then, about 800 bulls have beenevaluated each year (N. Reinsch, personalcommunication). Only bulls and bull damsare genotyped as tissue samples are alreadycollected for paternity testing. Thus additionalcosts due to MAS are low and evena very modest genetic gain can be economicallyjustified. This scheme is similar to the“top-down” scheme of Mackinnon andGeorges (1998) in that evaluation of thesons is used to determine which grandsiresare heterozygous for the QTL and theirlinkage phase. This information is thenused to select grandsons based on whichhaplotype was passed from their sires. Itdiffers from the scheme of Mackinnon andGeorges (1998) in that the grandsons arepreselected for PT based on MA-BLUPevaluations, which include general pedigreeinformation in addition to genotypes.The French MAS programme includeselements of both the “top-down” and“bottom-up” MAS designs. Similar to theGerman programme, genetic evaluationsincluding marker information were computedby a variant of MA-BLUP, andonly genotyped animals and non-genotypedconnecting ancestors were includedin the algorithm. Genotyped females werecharacterized by their average performancebased on pre-corrected records (with theappropriate weight), whereas males werecharacterized by twice the yield deviationof their non-genotyped daughters. Twelvechromosomal segments, ranging in lengthfrom 5 to 30 cM, are analysed. Regionswith putative QTL affecting milk productionor composition are located on BTA 3,6, 7, 14, 19, 20 and 26; segments affectingmastitis resistance are located on BTA 10,15 and 21; and chromosomal segmentsaffecting fertility are located on BTA 1, 7and 21. Each region was found to affect oneto four traits and on average three regionswith segregating QTL were found for eachtrait. Each region is monitored by two tofour evenly spaced microsatellites, and eachanimal included in the MAS programme isgenotyped for at least 43 markers. Sires anddams of candidates for selection, all maleAI ancestors, up to 60 AI uncles of candidates,and sampling daughters of bull siresand their dams are genotyped. The numberof genotyped animals was 8 000 in 2001 and50 000 in 2006. An additional 10 000 animalsare genotyped per year, with equalproportions of candidates for selection andhistorical animals.Future prospective for MAS indairy cattleAlthough the first large experiment inQTL detection in dairy cattle was publishedin 1961 by Neimann-Sørensen andRobertson, in 1985 it still looked as if