title: Gene mapping and chromosome 21: history and methodology.
mesh_terms: D002874:Chromosome Mapping; D002904:Chromosomes, Human, 21-22 and Y; D004314:Down Syndrome / Q000235:genetics* / Q000266:history; D004798:Enzymes / Q000235:genetics; D005819:Genetic Markers; D049673:History, 20th Century; D006801:Humans; D008722:Methods; D011110:Polymorphism, Genetic
chemical_list: D004798:Enzymes; D005819:Genetic Markers