Dr. Jack Dekkers
Dept. of Animal Science
Iowa State University
Genetic improvement of livestock primarily focuses on selection for
quantitative traits in outbred populations. To date, most genetic
improvement has been achieved through selection on breeding values
estimated from phenotype of the individual and/or its relatives.
Molecular genetics is now providing tools to enhance rates of genetic
improvement by being able to select on quantitative trait loci (QTL) or
on linked markers. Sophisticated statistical methods have been developed
to estimate the effects of QTL in complex pedigrees. The use of this QTL
information in strategies for marker-assisted selection (MAS) has,
however, received less attention. This is best illustrated by recent
simulation studies (e.g. Gibson, 1994, Proc. Wld. Congr. Genet. Appl.
Livest. 21:201), which showed that, although current strategies for MAS
on a known QTL increase response to selection in the short term, they can
lead to less response in the longer term than selection based on
phenotype. Reduced longer term response is caused by the impact of
increased emphasis on the known QTL on response in other genes that
affect the trait. We (Dekkers and van Arendonk, 1998, Genetical Research
71:257) recently developed methods to optimize selection on a known QTL.
Results show that QTL information can lead to greater responses to
selection in both the short and longer term, in particular for QTL that
exhibit dominance, provided selection on the QTL is optimally balanced
with selection on phenotypic information. Implications for strategies for
MAS and the benefits that can be expected from MAS in livestock breeding
programs will be discussed.
This material was presented
on Plant & Animal Genome VII held at St. Diego
(January 18-22, 1999) and Dr. Jack Dekkers was an invited