Trait correlations are common phenomena in biology. Plant breeders need to consider trait correlations to either improve correlated traits simultaneously or to reduce undesirable side effects when improving only one of the correlated traits. Pleiotropy or close linkage are the two major reasons for genetic trait correlations and are often confounded at the level of quantitative trait loci or genes. With the progress of genetic and genomic approaches, discrimination of intragenic linkage from true pleiotropy is increasingly possible. This will substantially impact breeding strategies and will be helpful to understand the nature of trait correlations.
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