1. A method for determining a classifier, the method comprising: producing a first generation chromosome population of chromosomes, each chromosome having (i) a selected number of genes specifying a sub-set of an associated set of measurements and (ii) an expressed sub-set-size gene having a value distinguishing expressed and unexpressed genes of the chromosome; computationally genetically evolving the genes of the chromosomes including the expressed sub-set-size gene respective to a fitness criterion evaluated without reference to unexpressed genes to produce successive generation chromosome populations; and selecting a classifier that uses the sub-set of associated measurements specified by the expressed genes of a chromosome identified by the genetic evolving.