Some further data on the H -2 system of antigens

The number of antigenic components detectable in system s such as H-2 in mice depends in part upon technical developments. It is also limited by the number of genetically different individuals available for study and a formula for deducing the number of antigenic components detectable for N unrelated systems is given in the text. If parental types and descendants derived from them by crossing over are included the possibilities are decreased. A new antigenic factor(s) has been brought to light by technical improvements and two more have been revealed by crossing over. Three cross-over combinations H-2g, H-2h and H-2i are now available as homozygotes. A preliminary map gives the order DCVK for genes within the H-2 system. The relative positions of E and K are not yet known but their genes are closely linked. The frequency of recombination between D and K was 1⋅03% for both sexes and 1⋅4% for females. Values obtained by other workers are given in the text. It is concluded that crossing over must make a material contribution to the polymorphism of the H-2 system. No convincing example of mutation within the system has been published as yet. One new cross-over system H-2i appears to have certain selective disadvantages whilst statistical evidence strongly indicates that H-2b, H-2d and H-2k are favoured by selection under laboratory conditions.