Tyr208 is converted to a stop codon by a single C-to-A point mutation in the b1 allele (Lamason et al., Science 310: 1782-1786, 2005).The RFLP assay (Restriction Fragment Length Polymorphism; Botstein et al., Am. J. Hum. Genet. 32: 314-331, 1980) is used to genotype the b1 allele. This method is used to detect a mutation that either creates or eliminates a restriction enzyme-recognized site. The RFLP assay begins with PCR-amplifying a sequence of interest, followed by restriction enzyme digestion of the PCR product. The resulting restriction pattern determines whether or not the mutation exists. The b1 mutation creates a site that the MseI restriction enzyme recognises.