In wild mice from Kitty Hawk, N. C., two new heavy chain linkage groups, G^3,5,7,8H^9,11F^fA^- and G^3,5,8H^9,11F^fA^-, were found, each of which genetically controls both the 3 and 5 distinct immunoglobulin determinants. In inbred strains the 3 and 5 determinants are found independently. The new heavy chain allotype G^3,5,7,8H^9,11F^fA^- probably arose from a homologous (intragenic) cross-over between G^3,8H^9,11F^fA^- and G^5,7,8H^9,11F^fA¹⁴ heavy chain linkage groups. It was suggested that genes controlling G^3,8G^5,7,8, G^3,5,8, and G^3,5,7,8 are alleles.

Another homozygous wild mouse (Kyushu, Japan) showed a new heavy chain allotype, ²G^1,6,7,8H^9,16F^sA¹⁵. The 2 and G^1,6,7,8 determinants are also separated in inbred strains. The 2 determinant in inbred mice is not on the F, H, or A heavy chain and is probably on a G or G-like immunoglobulin heavy chain. Papain digestion of serum from the Kyushu mouse showed two electrophoretically different Fc fragments, one carrying the G^1,6,7,8 and the other the 2 determinant. The new heavy chain allotype, ²G^1,6,7,8H^9,16F^sA¹⁵, of the Kyushu wild mouse probably arose from a nonhomologous (unequal) cross over between ²G^-H^9,16F^sA¹⁵ and G^1,6,7,8H^9,11F^fA^12,13,14 heavy chain linkage groups. The linkage group of the Kyushu wild mouse has at least five heavy chain genes, while that of the inbred mice has four.