Rgcs1 is a Mendelian-dominant locus affecting ganglion cell susceptibility to optic nerve crush. The mean (± s.d.) cells remaining for F2 mice were plotted as a function of inheritance of the D5Mit245 polymorphic marker. This marker is closest to the predicted location of chromosome 5 with the highest LOD score. Mice homozygous or heterozygous for the DBA/2J allele (D) have statistically equivalent phenotypes (t-test, P = 0.169), while mice that have inherited 2 BALB/c alleles (C) have significantly fewer cells remaining compared to F2 mice carrying a D allele (P = 4.4 × 10-7). These C/C mice exhibit a phenotype that is similar to the susceptible phenotype of the BALB/c parental strain.