Abstract
Out of 230 mice 89 (38.7%) have so far developed renal disease. Surviving mice range in age from 324-431 days. From studies on the age incidence of renal disease in NZB x NZW F1 hybrids it is to be expected that few of the backcross mice will develop renal disease when older than 400 days. Therefore the final proportion of mice developing renal disease seems likely to be between 40 and 50%. This suggests that only 2 dominant genes are involved, one contributed from each parent strain. A table shows that 113 of the mice (49%) were homozygous at the H 2 gene complex and 117 (51%) were heterozygous. If there were no linkage between H 2 genes and the genes controlling development of renal disease then 50% of mice with renal disease would be expected to be heterozygous at the H 2 complex and 50% homozygous. However, of the 89 mice which have so far developed renal disease 64 (72%) were heterozygous and 25 (28%) were homozygous. This difference is statistically significant chi2=25.7; P < 0.001) and indicates that the gene controlling renal disease and contributed by the NZB strain is linked to the H 2 complex. The apparent 28% crossover frequency between H 2 and the gene controlling renal disease suggests that they are quite widely separated on the same (17th) chromosome.