Prior to discovery of the c-Kit receptor and its ligand SCF, mice with double mutations at the ckit-encoding W loci (W/Wv mice) or scf-encoding Sl loci (Sl/Sld mice) were known to exhibit hypoplastic, macrocytic anemia, sterility, and a lack of cutaneous melanocytes (13–15). The gene discussed is KITLG; the disease is anemia (phenotype).