Quantitative genetics

Positional candidate cloning of a QTL in dairy cattle: identification of a missense mutation in the bovine DGAT1 gene with major effect on milk yield and composition. Grisart, B. et al. Genome Res. 12, 222–231 (2002) [PubMed]

Most economically important traits in livestock are quantitative — they are influenced by many genes and by their interaction with the environment. This paper reports the positional cloning of a major quantitative trait locus (QTL) for milk yield and composition in dairy cattle. The authors believe that the magnitude of this QTL could be attributable to a single mutation in one gene: they have identified a non-conservative missense mutation in DGAT1, a strong positional candidate gene that lies in the mapped interval and which prevents lactation when it is knocked out in mice.

Signal transduction

An allelic series at the PDGRα locus indicates unequal contributions of distinct signaling pathways during development. Klinghoffer, R. A. et al. Dev. Cell 2, 103–113 (2002) [PubMed]

It is an aim of the signal-transduction field to determine which signalling proteins enable receptor tyrosine kinases (RTKs) to stimulate specific signalling pathways during development. To investigate this, Klinghoffer et al. generated knock-in mice that carry mutations in the Pdgfra (platelet-derived growth-factor-receptor-α) gene, which selectively prevent this RTK from activating two of its target signalling proteins, PI3 kinase and Src kinase. Their findings show that loss of PI3 kinase activation leads to neonatal lethality due to impaired signalling in many cell types, whereas loss of Src activation affects only oligodendrocyte development.

Evolution

Genetic variation for phenotypically invariant traits detected in teosinte: implications for the evolution of novel forms. Lauter, N. & Doebley, J. Genetics 160, 333–342 (2002) [PubMed]

Single-gene mutations can radically alter the morphology of an organism, but is this the mechanism by which taxa evolve, or do new character traits arise, as some propose, by many, small-effect genes that bring the population towards towards a certain threshold? The authors have tested a prediction of the latter idea by examining the standing genetic variation in traits that are invariant in teosinte, but in which teosinte differs from its modern relative — maize. The presence of phenotypically silent genetic variation in teosinte supports the multiple-gene theory that selection has acted on many loci during the domestication of this crop.