QTL ANALYSIS IN PLANTS - WHERE ARE WE NOW

We have briefly reviewed the methods currently available for QTL analy sis in segregating populations and summarized some of the conclusions arising from such analyses in plant populations. We show that the anal ytical methods locate QTL with poor precision (10-30 cM), unless the h eritability of an individual QTL is high. Also the estimates of the QT L effects, particularly the dominance effects tend to be inflated beca use only large estimates are significant. Estimates of numbers of QTL per trait are generally low (<8) for individual trials. This may sugge st that there are few QTL but probably reflects the power of the metho ds. There is no large correlation between the numbers of QTL found and the amount of the variation explained. Of those cases where dominance is measurable, dominance ratios are often >1, but seldom significantl y greater. These latter cases need further analysis. Many QTL map clos e to candidate genes, and there is growing evidence from synteny studi es of corresponding chromosome regions carrying similar QTL in differe nt species. However, unreliability of QTL location may suggest false c andidates.