Despite this, tongue rolling is probably the most commonly used classroom example of a simple genetic trait in humans. 1971), which is additional evidence that there is some genetic influence on this trait.įamily studies clearly demonstrate that tongue rolling is not a simple genetic character, and twin studies demonstrate that it is influenced by both genetics and the environment. Dizygotic twins were twice as likely to differ in tongue-rolling ability as monozygotic twins (Reedy et al. (1971) and Martin (1975) also found numerous pairs of monozygotic twins who differed in tongue rolling. This clearly establishes that there are important non-genetic influences on tongue rolling, and it convinced Sturtevant (1965) that tongue rolling was not determined solely by genetics. Matlock (1952) found that out of 33 pairs of monozygotic (identical) twins, 7 pairs consisted of one R and one NR twin. The discrepancy could be due to more complicated genetics, involving multiple alleles or multiple genes, or some kind of environmental influence. Both studies found rolling offspring of non-rolling parents, so the trait must be more complicated than the myth says. However, if this trait were a simple one-gene, two-allele genetic character, with rolling completely dominant to non-rolling, then two non-rolling parents could not have a rolling child. It is difficult to imagine how the common family environment could influence tongue-rolling, so this resemblance between relatives suggests that there is a large genetic influence on tongue-rolling. In both family studies, individuals with tongue-rolling parents are much more likely to be tongue-rollers than individuals with non-rolling parents. Komai (1951) performed a similar study with much larger sample sizes, and found similar results: Parents He concluded that tongue rolling was at least partially genetic, with rolling dominant to non-rolling, despite the four R offspring of NR x NR parents. Sturtevant (1940) compared parents and offspring, with the following results: Parents There are also some people who can only slightly roll the edges of their tongue and cannot easily be classified as rollers or non-rollers (Reedy et al. That some people learn to roll their tongues after first being unable to is the first evidence that this is not a simple genetic character. ![]() Komai (1951) found that the proportion of tongue-rollers among Japanese schoolchildren increased from 54 percent at ages 6-7 to 76 percent at age 12, suggesting that over 20 percent of the population learns to tongue-roll during that age range. However, some people, especially children, cannot roll their tongue when first asked but later learn to do so (Sturtevant 1940). The proportion of people who can roll their tongue ranges from 65 to 81 percent, with a slightly higher proportion of tongue-rollers in females than in males (Sturtevant 1940, Urbanowski and Wilson 1947, Liu and Hsu 1949, Komai 1951, Lee 1955). Most people, when first asked, either can easily roll their tongue (here called "R"), or cannot roll it at all ("NR"). The reality Tongue rolling as a character Many studies have shown that the myth is incorrect, but tongue rolling remains a popular subject in genetics classes. Alfred Sturtevant (one of the pioneers of Drosophila genetics) described tongue rolling as a simple two-allele character, with the allele for rolling (usually given the symbol T or R) being dominant over the allele for non-rolling (t or r) (Sturtevant 1940). ![]() This is one of the most common traits that biology teachers use to demonstrate basic genetic principles. ![]() Some people can roll their tongue into a tube, and some people can't.
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