Program of Computational Genomics, CIFN, UNAM, A.P. 565-A, Cuernavaca, Morelos 62100, Mexico. moreno@cifn.unam.mx|Program of Computational Genomics, CIFN, UNAM, A.P. 565-A, Cuernavaca, Morelos 62100, Mexico. moreno@cifn.unam.mx