A Successful Marriage: Making the Transition from Quantitative Trait Locus Mapping to Marker-Assisted Selection (Also published on-line in AgBiotechNet at URL http://agbio.cabweb.org)

The change from a Mendelian to a genomic breeding paradigm poses three challenges: to map the components of animal breeding onto a genomic conceptual frame work; to show how the genetic parameters comprising a genomic analysis can be obtained from actual farm data; and to show how genomic parameters can guide a breeding program. We are currently heavily engaged in the second challenge, but should start thinking seriously about the third. Negotiating the shift to marker assisted selection (MAS), will involve: (1) Determining marker-QTL phase (a QTL for which this has been achieved will be termed a "Marked QTL, MQTL"); (2) Tracing MQTL across the generations; (3) Incorporating MQTL in the existing selection program by identifying and creating a "selection space"; (4) Changing the existing selection program to enable more effective utilization of MQTL; and (5) Expanding reproduction opportunities to further exploit MAS. These components are discussed in some detail and applied to MAS programs in dairy cattle and layer chickens.