Genes for quantitative traits in domestic animals

Genes for quantitative traits in domestic animals
Leif Andersson
Department of Medical Biochemistry and Microbiology, Uppsala University, BMC,
Box 597, S-751 24 Uppsala, Sweden
A huge number of QTLs have by now been documented in domestic animals. However,
as in other species the identification of the genes underlying QTLs is very challenging.
Despite considerable efforts, the causal genes for only a handful QTLs have been
described so far. The most prominent examples being a single nucleotide substitution in
intron 3 of IGF3 affecting postnatal muscle growth in pigs and a single nucleotide
substitution in the 3’UTR of MSTN, creating a new target site for two microRNAs, which
underlies a QTL for muscularity in sheep. So why is the identification of QTL mutations
so difficult? One obvious reason is the difficulty in getting a sufficient map resolution (<1
Mbp) that makes it possible to resequence and evaluate all transcripts in the QTL region
as regards their coding sequence and regulatory elements. Another complicating factor is
that a good proportion of QTLs have a complex architecture where mutations in two or
more closely linked genes and/or two or more mutations in the same gene cause the QTL.
Epistatic interaction further complicates the analysis. However, the extensive use of
linkage combined with linkage disequilibrium mapping hold the promise to make
positional identification of QTL mutations more feasible in the future. My prediction is
that a majority of these mutations will constitute tissue-specific regulatory mutations and
this notion is supported by our recent identification of mutations underlying monogenic
trait loci in dogs, horses and chicken.