Article mis-states the yeast convention Ken Wolfe, Trinity College Dublin 1 March 2011 The article mis-states the yeast convention. The Watson strand is the strand with its 5' end at the left telomere, but the left arm is not always the shorter arm of a yeast chromosome. In fact, the L arm is longer than the R arm for 7 of the 16 yeast chromosomes (up to 4 times longer, in the cases of chromosomes IX and XIV). The left/right nomenclature for yeast chromosome arms dates back to the early days of yeast genetic maps, but I do not know who introduced it. Cytogenetics is not really possible for Saccharomyces because the chromosomes are too small and do not have extensive heterochromatin at centromeres, so nobody knew which arm was the shorter one until chromosome-sized genetic (and eventually genomic) maps became available. Oliver et al (Nature 357:38, 1992) then used the well established genetic conventions (chromosome numbering and L/R arm nomenclature) when they published the first yeast chromosome sequence. They chose the name Watson for the strand that has its 5' end at the left telomere. Competing interests None.