MGI:96885This locus controls an antigen on thymocytes, lymphocytes and bone marrow cells. The a allele determines Ly9.1 antigen in A/J, 129/Re, BALB/c and C3H/He; the b allele determines antigen Ly9.2 in the C57 family of strains, HTI/Go, MA/My, F/St and C58/Lw. Null mutants are viable, healthy and fertile.