Fred Hutchison Cancer Research Center, Program Computational Biology,1100 Fairview Avenue North P. O. Box 19024, Seattle, WA 98109, USA. sfalcon@fhcrc.org|Fred Hutchison Cancer Research Center, Program Computational Biology,1100 Fairview Avenue North P. O. Box 19024, Seattle, WA 98109, USA. sfalcon@fhcrc.org