Chromosome variants (= markers) are segments of variable length and staining properties which do not exert an apparent impact on the phenotype of the person. These variants mainly include centromeric segments on chromosomes 1, 3, 4, 9, 13-15, 21, 22 and the distal long arm of the Y chromosome. Individual markers differ by their variable length and fluorescence intensity following Q-staining. Inheritance is dominant, and fresh mutations occur very rarely indeed. Markers can be used for the following purposes: To demonstrate the take of a bone marrow transplant; to determine zygosity in like-sexed twins and paternity (both already feasible during the fetal period); to determine maternal versus paternal origin of additional chromosomes (trisomies), of de novo structurally altered chromosomes, and of haploid sets in triploidy and chimerism.