Abstract
Two of the antigenic characters of erythrocytes, that in either identical or related forms differentiate four species of Streptopelia (chinensis, humilis, orientalis, and senegalensis) from a fifth (S. risoria) by interaction of the causative genes, are involved in the appearance in backcross hybrids of additional antigenic specificities to those of the parental species. The cells of backcross hybrids, resulting from matings of S. chinensis x S. risoria and backcrossing to S. risoria, in which the two independently inherited antigenic characters (ch-4 and ch-8 peculiar to S. chinensis) are combined as homozygotes, exhibit an antigenic specificity not present in backcross birds carrying separately these two characters. This result indicates an interaction within S. chinensis of the genes for these two antigenic characters. An antigen (C(g)) by which Columba guinea differs from C. livia has behaved as a unit in over 400 backcross offspring. It is antigenically related to both ch-4 and ch-8 of S. chinensis. It is also related to, but not identical with, this interaction antigen of S. chinensis. Further, the C(g) character is also related to an interaction product that appears in all backcross offspring carrying the group-4 antigen in a S. risoria genome. Genes related to those that in modern species or in species hybrids interact to effect new antigenic specificities presumably possessed the same abilities in ancestral forms of Columbidae.