Eaten sweet potato? Then you’ve had a GM meal | Letters

The sweet potato (commonly called a yam) is a familiar vegetable on our supermarket shelves and it is indeed an achievement to grow the sweet potato in the UK (British farmers crack the sweet potato, 18 October). The sweet potato is eaten by some billion people worldwide and is high in vitamins A and C and fibre as well as starch.

If you too have eaten sweet potato you have eaten your first GM meal. Some 8,000 years ago a bacterium (Agrobacterium) inserted two of its genes into the original sweet potato DNA thus producing a GM sweet potato. These genes have been detected in some 300 varieties of "yam"; they are expressed and cause tissues like the root to swell. Domestication was probably based on root size and thus continued propagation of its GM variety.