For example, the component viral strains of the MMR (measles, mumps, rubella) vaccine were developed in either embryonated hens’ eggs or chick embryo cell cultures (measles and mumps) and human WI-38 cells derived from embryonic lung tissue (rubella) to allow for production of more virus and attenuation through growth and passage in non-human cells or cell culture. The gene discussed is MRC1; the disease is measles.