CROSSING OVER BETWEEN GENES IN THE IMMUNOGLOBULIN HEAVY CHAIN LINKAGE GROUP OF THE MOUSE

Immunoglobulin heavy chain genes were found in wild mice (Mus musculus) that could best be explained as recombinants of immunoglobulin genotypes.

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 γF, γH, or γA heavy chain and is probably on a γG or γG-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.