(Science: molecular biology) The method used to identify the number of sets of chromosomes within a cell or organism (i.e. Its ploidy). Each set is designated n so one set is n is haploid, two sets is 2n is diploid, three sets is 3n is triploid, four sets is 4n is tetraploid, etc. Also, 2n_1 is known as trisomy (i.e. Two full sets plus a third copy of one of the chromosomes).