Peter Goodfellow. Portrait of Peter Goodfellow, the British geneticist who led the team that disc- overed the mammalian sex-determining gene, Sry. Goodfellow, head of the Department of Genetics at Cambridge University, studied mouse foetuses. He found that Sry's effect on the genitals of the foetus was to begin the development of the testes. Sry is part of the male (Y) chromosome. He has also shown that the combination of several defect- ive genes can lead to the development of multiple sclerosis, but also that not all genetically- susceptible people develop the disease. Photographed in 1997.