According to recent research, being partial to a cup of coffee could all be in your genes. Research by Craig Montell and his colleagues at Johns Hopkins University has identified the first known receptor cells for caffeine. This research appeared in the September 19th issue of Current Biology. A study was carried out on fruit flies and it was found that a single protein determines whether fruit flies eat sugar laced with caffeine or avoid the bitter taste of the caffeine. Researchers studied how taste-receptor mutations impacted the behaviour of fruit flies. They showed that a specific taste receptor, known as Gr66a, is responsible for the perception of caffeine's bitter taste by fruit flies. When the gene encoding the Gr66a receptor was disrupted, the mutant flies failed to react normally to the presentation of caffeine, which is a bitter compound that flies are averse to eating. Flies that had an intact Gr66a receptor gene had a much stronger preference for sucrose (sugar) consumption when given a choice between sucrose and a mixture of sucrose and bitter compounds. However when the scientists removed the Gr66a gene from the flies, the flies overcame their dislike of caffeine. Without this Gr66a protein, the flies seemed unable to taste the caffeine. Scientists have not discovered whether Gr66a has a similar effect in humans. However the discovery of a caffeine receptor does suggest that a taste for coffee is likely to be affected by genes.