Polymorphism, Linkage and the Blood Groups

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Abstract
Animals polymorphic for a number of color patterns or other characters often have linkage between many of the genes responsible for the polymorphism. Most examples of polymorphism associated with linkage have a number of other points in common. Different combinations of genes have different selective values, the linked genes control a similar type of character (e.g. pigmentation); there is frequently a common "universal recessive", and several related spp. are often polymorphic for similar characters. In most of these respects the blood groups are similar to the polymorphism for color patterns found in insects, snails and fish. It is suggested that the linkage groups evolved as the result of selection for increased linkage between genes affecting each others selective value. Genes originally on different chromosomes will in the course of time be brought on the same chromosome by selection for suitable translocations. After this, recombination will be further reduced by selection for shifts and inversions increasing the linkage as well as the suppression of chiasma formation.