To determine the basic chromosome number (x) of an allopolyploid species, you need to identify the diploid chromosome number (2n) of the allopolyploid and then divide that number by the ploidy level (the number of complete sets of chromosomes) of the species, which can be inferred by analyzing the chromosome pairing behavior during meiosis and comparing it to the known chromosome numbers of the parental species involved in the hybridization event that created the allopolyploid; essentially, x = 2n / ploidy level.