A<unk>  is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be observed. A<unk>  may be a short DNA sequence, such as a sequence surrounding a single base-pair change (single nucleotide polymorphism, SNP), or a long one, like minisatellites.
Genetic marker
Biomarker
Biomarker 
Lineage markers
Milch classification
Disposition index
Triple test score
Herbert classification