Abstract
An earlier genetic mapping study with an unidentified Russian Wheat Aphid resistance gene, referred to as Dn? and derived from PI 294994, suggested that the gene occurs close to the centromere on 7DS. Closer inspection of the map data showed that mild segregation distortion occurred at some of the loci (including Dn? which could have affected conclusions regarding the gene order. As a result, and depending on the gene order inferred in the analysis, Dn? could be mapped on either side of the 7D centromere. A telosomic analysis was therefore undertaken in order to confirm the map position or to determine the true location of Dn? However, physical mapping showed that Dn? was not even located on chromosome 7D and it was concluded that it may be the same gene as Dn4 on 1DL. The result cautions that even mildly distorted segregation data could be very misleading and that genetic mapping results based on such data need to be confirmed independently, preferably by physical mapping.
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