QTL mapping under truncation selection in homozygous lines derived from biparental crosses |
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Authors: | Email author" target="_blank">Albrecht?E?MelchingerEmail author Elena?Orsini Chris?C?Sch?n |
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Institution: | 1.Institute of Plant Breeding, Seed Science, and Population Genetics,University of Hohenheim,Stuttgart,Germany;2.Plant Breeding, Center of Life and Food Sciences Weihenstephan,Technische Universit?t München,Freising,Germany |
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Abstract: | In plant breeding, a large number of progenies that will be discarded later in the breeding process must be phenotyped and
marker genotyped for conducting QTL analysis. In many cases, phenotypic preselection of lines could be useful. However, in
QTL analyses even moderate preselection can have a significant effect on the power of QTL detection and estimation of effects
of the target traits. In this study, we provide exact formulas for quantifying the change of allele frequencies within marker
classes, expectations of marker contrasts and the variance of the marker contrasts under truncation selection, for the general
case of two QTL affecting the target trait and a correlated trait. We focused on homozygous lines derived at random from biparental
crosses. The effects of linkage between the marker and the QTL under selection as well as the effect of selection on a correlated
trait can be quantified with the given formulas. Theoretical results clearly show that depending on the magnitude of QTL effects,
high selection intensities can lead to a dramatic reduction in power of QTL detection and that approximations based on the
infinitesimal model deviate substantially from exact solutions. The presented formulas are valuable for choosing appropriate
selection intensity when performing QTL mapping experiments on the data on phenotypically preselected traits and enable the
calculation and bias correction of the effects of QTL under selection. Application of our theory to experimental data revealed
that selection-induced bias of QTL effects can be successfully corrected. |
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