Three genetic loci in the mouse affect the synthesis and assembly of the erythrocyte membrane skeleton. The spherocytosis and jaundiced loci affect the membrane skeletal protein known as spectrin. The normoblastosis locus affects the spectrin binding protein called ankyrin. We have obtained genetic data that define the linkage relationships among three spectrin genes and the spherocytosis and jaundiced loci. The erythroid alpha-spectrin gene is tightly linked to the spherocytosis locus on chromosome 1 and the jaundiced locus is on chromosome 12, tightly linked to the erythroid beta-spectrin gene. The brain alpha-spectrin (alpha-fodrin) gene is located on the centromeric end of chromosome 2 and is not closely linked to any previously mapped erythroid or neurological mutation. These results are consistent with the hypothesis that defects in the alpha- and beta-spectrin genes cause the spherocytosis and jaundiced hemolytic anemias in mice. All five loci studied are located within chromosomal segments that are conserved between mouse and man. Analysis of the data from the chromosome 12 study defines a new order for the genes on that chromosome and delineates the largest mouse/human conserved chromosomal segment yet known.