Segments of chromosomal DNA known to be linked with heritable traits or diseases. Although the markers themselves do not produce the conditions, they exist in concert with the genes responsible and are passed on with them. Certain markers, restriction fragment length polymorphisms (RFLPs), consist of segments of DNA that can be identified on autoradiographs (produced after digestion of the DNA by restriction enzymes and segregation of the resulting fragments through gel electrophoresis).