Cytotaxonomy is the branch of biology dealing with the relationships and classification of organisms using comparative studies of chromosomes.
The number, structure, and behaviour of chromosomes is of great value in taxonomy, with chromosome number being the most widely used and quoted character. Chromosome numbers are usually determined at mitosis and quoted as the diploid number (2n), unless dealing with a polyploid series in which case the base number or number of chromosomes in the genome of the original haploid is quoted. Another useful taxonomic character is the position of the centromere. Meiotic behaviour may show the heterozygosity of inversions. This may be constant for a taxon, offering further taxonomic evidence. Cytological data is regarded as having more significance than other taxonomic evidence.