Chromosome studies in African wild pigs (Suidae, Mammalia).

The chromosomes of the giant forest hog, Hylochoerus meinertzhageni, the warthog, Phacochoerus aethiopicus and the bush pig, Potamochoerus porcus are studied. Their sex- and nucleolar chromosomes are compared mutually and with those of the domestic pig, Sus scrofa. All four species have similar X and Y chromosomes. The only bush pig sow examined, however, exhibits an extraordinary situation with two very different X chromosomes. One of these X's, which is of the ordinary type, is present in the boars together with a Y. Each species has two pairs of nucleolar chromosomes, which resemble each other in all the pigs studied. Secondary constrictions and silver staining may appear in one or in both the members of these pairs near the centromeres. Robertsonian translocations probably occurred during the differentiation of all the chromosome complements. More complex chromosomal rearrangements, however, are needed to explain the evolution of the chromosome set of the bush pig.