Possible artifactual gains and losses due to reconciliation between an incorrect gene tree and a correct species tree. (a) Gene trees with a single eutherian species (a
) on one side of a duplication node (red dot) and several species on the other side (especially if a
is absent from that side) are highly suspicious (Table 1). Such an incorrect gene tree will gen-erate one false duplication on the basal eutherian lineage followed by multiple false losses (vertical green and oblique blue bars). (b) Average duplication confidence (and standard de-viation) for all duplication nodes on all 26,467 gene trees from the ENSEMBL version 49 da-tabase. The eutherian node is highlighted in red.