Sir Ralph Riley FRS was a British geneticist.
He was born in Scarborough, North Yorkshire in 1924 and served in the army during the Second World War. After the war he studied Botany at Sheffield University, followed by a two year PhD study in genetics.
He was then recruited by the Plant Breeding Institute at Cambridge to study the introduction of useful variation into the wheat crop from its wild relatives. Two years later in 1954 Riley became the founder and first Head of the Cytogenetics Department at the PBI. His target was to increase the wheat gene pool by making the variation in wild relatives available to wheat breeders. In 1957, he discovered the method of doing so by finding the Ph gene. This gene controlled the pairing between the chromosomes of wheat and wild relatives of wheat and soon he was able to demonstrate the cytogenetic ways by which useful genes, such as those that confer novel disease resistances, could be transferred into wheat from a host of wild species. This discovery of the Ph gene allowed the first "genetic engineering" and his methods have since been used around the world in all major cereal breeding programmes.