Is Tongue-Rolling a Genetic Trait?

          "How many people in this room can roll their tongue?" This question was posed to my ninth grade biology class as an introduction to the subject of genetic traits. I was taught that tongue-rolling, the ability to elevate the lateral edges of the tongue, was a genetic trait; thus, if you were able to roll your tongue, at least one of your parents would be able to do the same. This example was widely utilized in schools to introduce children to the concept of genetic inheritance, but can this trait be  explained by a single gene?

          Several studies in the past 70 years have set out to answer this question. Alfred Sturtevant, of later Drosophila melanogaster (fruit fly) genetics fame, was scintillated by this question and conducted a small survey on those able to roll their tongue (rollers) and those that could not roll their tongue (non-rollers) within families. Before embarking on this project, he hypothesized that tongue-rolling was determined by a single gene with two copies (one inherited from each parent). During his studies, he found that tongue-rolling parents often had children with the same trait. However, he also discovered that parents without the tongue-rolling trait occasionally had children that rolled their tongues, albeit at a lower frequency than parents with the trait. Philip Matlock conducted a similar study in identical twins across a large age range and noted many cases in which only one twin was a tongue roller. The data collected by Sturtevant, Matlock, and others suggest that tongue-rolling cannot be attributed to one gene. In fact, this trait can also be learned because in 1951, Taku Komai's analysis of Japanese children described the increase in tongue-roller frequency from 54% in children from ages 6-7 to 76% in children at age 12.

Courtesy: fakescience.org

        Since there is overwhelming evidence that tongue-rolling is not controlled by a single gene, what are the other possibilities? One is that tongue-rolling is determined by multiple genes, so it would be quite complex to predict who possesses this trait since the identity and quantity of genes responsible for this trait are unknown. Another is that this trait requires an environmental component, and this would be compatible with the observation that non-rollers can learn to roll their tongues. In light of this data, it is inaccurate to state that tongue-rolling is a simple genetic trait. Therefore, it would be more wise for classrooms to revert to pea color and shape as examples of Mendelian inheritance.