marker-assisted selection in wheat - ictsd

Chapter 13 – Marker-assisted selection in sheep and goats 241breeding programmes where commercialapplications are viable. The basic conditionis that ram breeders and ram buyers areprepared to pay for genetic informationarising from genetic testing. This is morelikely to happen in places where acrossflockgenetic evaluations already exist,combined with objective trait measurementand trait valuation in the form of indices.However, not all genetic information canbe translated into dollar index terms andgenetic testing is often valued beyond theexisting index framework.Experimental sheep MASThe purpose of “experimental MAS” programmesis to demonstrate that geneticchanges can be achieved based on genotypeselection and thereby to encourage uptakeof MAS by commercial breeders. Usually,the programmes are also designed eitherto estimate QTL effects more clearly, orto confirm earlier experimental results inindustry flocks. Examples of such MASprogrammes are:• selection of sheep against susceptibilityto scrapie, being conducted in France andthe United Kingdom;• the MAS Applied to Commercial Sheep(MASACS) Programme in the UnitedKingdom, coordinated by OswaldMatika from the Roslin Institute. Theresearch team in this programme collaborateswith commercial breeders. Threegene marker tests for muscling are beingtrialled in the first year and it is envisagedthat a test for parasite resistance will beintroduced in 2006. The three QTL aretermed “Texel muscling” (chromosome18), “Suffolk muscling” (chromosome 1)and “Charollais muscling” (chromosome1) as described by McRae et al. (2005),and the tests will be applied within therespective breeds.Commercial sheep MASCommercial gene testing in sheep is limitedmostly to service providers in NewZealand, mainly Ovita and the Universityof Lincoln, whereas it is absent in goats.Details about gene tests can be found onthe Australian Gene Mapping Web site(Maddox, 2005). Gene tests currently availableare:• Foot rot, a gene test commercialized bythe University of Lincoln;• Inverdale gene, through Ovita;• Booroola gene, through Genomnz;• Scrapie, (PrP gene), available throughmany companies (see Maddox, 2005);• Carwell gene, available through Ovita asLoinmax;• Texel Muscling gene (Chrom 2), availablethrough Ovita as MyoMax.None of these tests is currently integratedwith formal genetic evaluationsystems. Rather, gene test results and indexvalues based on polygenic quantitativetraits will have to be used separately, andholistic approaches are needed to deviseselection rules. The gene tests for reproductivetraits are not straightforward to use,while the Inverdale gene is only useful ina heterozygous state and requires specificcrossing programmes. The Booroola inheritancemodel is more straightforward butthe effect is too large for most managementsystems found in Australia.It should also be noted that most ofthe commercial gene tests are for traitsthat are not captured by formal EBVs, andcannot be incorporated easily into existingEBVs, e.g. gene tests for disease traits suchas scrapie and foot rot. In principle, thetests for muscle traits could be part of theEBV calculation, but from a ram marketingperspective it might be more useful to exploitthe genotype information obtained moreexplicitly. Furthermore, the proportion of