In 2018 the gene symbol Pgm1 was replaced with Pgm2 to be more consistent with human gene nomenclature. The recessive lethal Pgm2^b-m1Ehs allele was induced by triethylenemelamine treatment of a DBA/2J (Pgm2^b) male, which was then crossed to a C57BL/6J (Pgm2^a) female (Soares 1979). This mutation was imported from Dr. E. R. Soares into the laboratory of Dr. Eva Eicher at The Jackson Laboratory in 1979 and was maintained by breeding to C57BL/6J and C3H/HeJ (Pgm2^c) in alternating generations. A Pgm2^b-m1Ehs/Pgm2^a male was imported and mated to a C3H/HeJ female, then the Pgm2^b-m1Ehs/Pgm2^c offspring were mated to C57BL/6J and their Pgm2^b-m1Ehs/Pgm2^a offspring were bred to C57BL/6J. Compound heterozygotes were screened by cellulose acetate gel electrophoresis to determine genotype. This system of breeding continued until 1983 when embryos were generated for cryopreservation by breeding Pgm2^c/Pgm2^b-m1Ehs males with C57BL/6J females. The cryorecovered pups will be a mix of Pgm2^b-m1Ehs/Pgm2^a and Pgm2^a/Pgm2^c. To continue the line, the Pgm2^b-m1Ehs/Pgm2^a animals should be bred to C3H/HeJ (Pgm2^c) and the Pgm2^b-m1Ehs/Pgm2^c offspring should then be bred to C57BL/6J.