marker-assisted selection in wheat - ictsd

200Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishSummaryConsidering the long generation interval, the high value of each individual, the very limitedfemale fertility and the fact that nearly all economic traits are expressed only in females, itwould seem that cattle should be a nearly ideal species for application of marker-assistedselection (MAS). As genetic gains are cumulative and eternal, application of new technologiesthat increase rates of genetic gain can be profitable even if the nominal annualcosts are several times the value of the nominal additional annual genetic gain. Completegenome scans for quantitative trait loci (QTL) based on the granddaughter design havebeen completed for most commercial dairy cattle populations, and significant acrossstudyeffects for economic traits have been found on chromosomes 1, 3, 6, 9, 10, 14 and20. Quantitative trait loci associated with trypanotolerance have been detected in a crossbetween the African N’Dama and the Boran breeds as the first step in the introgressionof these genes into breeds susceptible to trypanosomosis. In dairy cattle, the actual DNApolymorphism has been determined twice, for QTL on BTA 6 and BTA 14. In both casesthe polymorphism caused a non-conservative amino acid change, and both QTL chieflyaffect fat and protein concentration. Most theoretical studies have estimated the expectedgains that can be obtained by MAS to be in the range of a 5 to 20 percent increase in therates of genetic gain obtained by traditional selection programmes. Applied MAS programmeshave commenced for French and German Holsteins. In both programmes geneticevaluations including QTL effects are computed by variants of marker-assisted best linearunbiased prediction (MA-BLUP).