[The Duffy system: a population genetics study in Portugal, Guinea-Bissau and Brazil]

2225 blood samples from Portugal (classed according to historical provinces), 301 blood samples from Guinea-Bissau (classed in tribes) and 697 blood samples from Brazil (classed according to colour of skin) have been tested in the Duffy system. The Portuguese seem to be a sufficiently uniform and autonomous population. This is also true for the (non-rejected) blood-samples from Guinea-Bissau. The Brazilians differ in accordance with their colour of skin. The expected relations between Portugal and its former colonies can be proved. The Duffy system is suited for the distinction of black and non-black populations and enables to recognize extraneous admixtures.