Tongue rolling is the ability to roll the lateral edges of the tongue upwards into a tube. The tongue's intrinsic muscles allow some people to form their tongues into specific shapes. Rolling the tongue into a tube shape is often described as a dominant trait with simple Mendelian inheritance, and it is commonly referenced in introductory and genetic biology courses, although there is some disagreement. [1]
Prevalence in human populations varies between 65% and 81%. [2]
There is no statistically significant sexual dimorphism in this trait. A 1940 study by Alfred Sturtevant analyzed 282 people of mostly European ancestry and observed that 67.1% of females and 62.9% of males could roll their tongues, and the remaining could not do it. [3] A 1980 study with 992 people also found similar percentages, in 66.84% of females and 63.7% of males possessing the ability. [4]
In some cases, the ability can be learned by practice, more easily by children, but also by adults. For this reason, studies should allow time for individuals to learn this and other abilities. This also indicates that it's not a simple hereditary trait, and there are other factors involved. [2] [3] [5]
In the first paper about this trait as a genetic trait, Sturtevant concluded that the ability "is conditioned at least in part by heredity", and suggests that "it is possible, though not proved, that ability to turn up the edges of the tongue may be due to a single dominant gene, with the fairly frequent occurrence of additional complications". [3] [6] These findings, however, have been questioned.
Several twin studies on the issue have been conducted. A 1952 study involving 33 pairs of identical twins found that 21% of them were discordant - that is, one of the twins had the ability and the other did not. [7] A 1971 study found that identical twins were 18% discordant, and 22% of non-identical twins were discordant, concluding that "hereditary factors strongly influences tongue rolling ability". [8] However, a 1975 found that identical twins were 28% discordant, while 31% of non-identical twins were discordant, and concluded that identical twins were no more likely than fraternal twins to both have the same phenotype for tongue rolling. [9]
One explanation for the pattern is that the trait has incomplete penetrance. That is, not every individual with the genes can express the trait. [10]
Cloverleaf tongue is the ability to fold the tongue in a certain configuration with multiple bends. This trait has been speculated by David D. Whitney in 1950 to be a dominant trait inherited separately from tongue rolling. [11]
Other tongue ability is folding the tip of the tongue upwards, which has been proposed as a recessive trait in a 1948 study, with possible epistatic interaction with the rolling gene. [5] [11]
Twisting the tongue has also been studied, which is to rotate the tongue approximately 90 degrees from the plane of the blade, both to the right and to the left. [5]
A 1980 study analyzed if there was any interaction between ear wiggling and tongue rolling, and found it to be the case for males, with men more likely to have both abilities or none, but no interaction was found for females. [4]
In This Is Us , an adopted teenager asks strangers to roll their tongues in an attempt to locate his biological family using genetics. [12]
In the Powerpuff Girls episode "Nuthin' Special", while searching for a unique super power not shared by her sisters, Buttercup finds out she is the only one that can roll her tongue. [13]
Gregor Johann MendelOSA was an Austrian-Czech biologist, meteorologist, mathematician, Augustinian friar and abbot of St. Thomas' Abbey in Brno (Brünn), Margraviate of Moravia. Mendel was born in a German-speaking family in the Silesian part of the Austrian Empire and gained posthumous recognition as the founder of the modern science of genetics. Though farmers had known for millennia that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity, now referred to as the laws of Mendelian inheritance.
The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific gene depends on the number of copies of each chromosome found in that species, also referred to as ploidy. In diploid species like humans, two full sets of chromosomes are present, meaning each individual has two alleles for any given gene. If both alleles are the same, the genotype is referred to as homozygous. If the alleles are different, the genotype is referred to as heterozygous.
Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.
Mendelian inheritance is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularized by William Bateson. These principles were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis.
The genotype–phenotype distinction is drawn in genetics. The "Genotype" is an organism's full hereditary information. The "Phenotype" is an organism's actual observed properties, such as morphology, development, or behavior. This distinction is fundamental in the study of inheritance of traits and their evolution.
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and the second is called recessive. This state of having two different variants of the same gene on each chromosome is originally caused by a mutation in one of the genes, either new or inherited. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes (autosomes) and their associated traits, while those on sex chromosomes (allosomes) are termed X-linked dominant, X-linked recessive or Y-linked; these have an inheritance and presentation pattern that depends on the sex of both the parent and the child. Since there is only one copy of the Y chromosome, Y-linked traits cannot be dominant or recessive. Additionally, there are other forms of dominance, such as incomplete dominance, in which a gene variant has a partial effect compared to when it is present on both chromosomes, and co-dominance, in which different variants on each chromosome both show their associated traits.
Penetrance in genetics is the proportion of individuals carrying a particular variant of a gene (genotype) that also expresses an associated trait (phenotype). In medical genetics, the penetrance of a disease-causing mutation is the proportion of individuals with the mutation that exhibit clinical symptoms among all individuals with such mutation. For example: If a mutation in the gene responsible for a particular autosomal dominant disorder has 75% penetrance, then 75% of those with the mutation will go on to develop the disease, showing its phenotype, whereas 25% will not.
Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics and in related fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.
Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart. In other words, the nearer two genes are on a chromosome, the lower the chance of recombination between them, and the more likely they are to be inherited together. Markers on different chromosomes are perfectly unlinked, although the penetrance of potentially deleterious alleles may be influenced by the presence of other alleles, and these other alleles may be located on other chromosomes than that on which a particular potentially deleterious allele is located.
Phenylthiocarbamide (PTC), also known as phenylthiourea (PTU), is an organosulfur thiourea containing a phenyl ring.
Carl Erich Correns was a German botanist and geneticist notable primarily for his independent discovery of the principles of heredity, which he achieved simultaneously but independently of the botanist Hugo de Vries, and for his acknowledgment of Gregor Mendel's earlier paper on that subject.
Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.
Alfred Henry Sturtevant was an American geneticist. Sturtevant constructed the first genetic map of a chromosome in 1911. Throughout his career he worked on the organism Drosophila melanogaster with Thomas Hunt Morgan. By watching the development of flies in which the earliest cell division produced two different genomes, he measured the embryonic distance between organs in a unit which is called the sturt in his honor. On February 13, 1968, Sturtevant received the 1967 National Medal of Science from President Lyndon B. Johnson.
In genetics, expressivity is the degree to which a phenotype is expressed by individuals having a particular genotype. Alternatively, it may refer to the expression of a particular gene by individuals having a certain phenotype. Expressivity is related to the intensity of a given phenotype; it differs from penetrance, which refers to the proportion of individuals with a particular genotype that share the same phenotype.
In genetics, concordance is the probability that a pair of individuals will both have a certain characteristic given that one of the pair has the characteristic. Concordance can be measured with concordance rates, reflecting the odds of one person having the trait if the other does. Important clinical examples include the chance of offspring having a certain disease if the mother has it, if the father has it, or if both parents have it. Concordance among siblings is similarly of interest: what are the odds of a subsequent offspring having the disease if an older child does? In research, concordance is often discussed in the context of both members of a pair of twins. Twins are concordant when both have or both lack a given trait. The ideal example of concordance is that of identical twins, because the genome is the same, an equivalence that helps in discovering causation via deconfounding, regarding genetic effects versus epigenetic and environmental effects.
Mendelian traits in humans are human traits that are substantially influenced by Mendelian inheritance. Most – if not all – Mendelian traits are also influenced by other genes, the environment, immune responses, and chance. Therefore no trait is purely Mendelian, but many traits are almost entirely Mendelian, including canonical examples, such as those listed below. Purely Mendelian traits are a minority of all traits, since most phenotypic traits exhibit incomplete dominance, codominance, and contributions from many genes. If a trait is genetically influenced, but not well characterized by Mendelian inheritance, it is non-Mendelian.
Dominant white (W) is a group of genetically related coat color alleles on the KIT gene of the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting, as well as bold white markings. Prior to the discovery of the W allelic series, many of these patterns were described by the term sabino, which is still used by some breed registries.
Oligogenic inheritance describes a trait that is influenced by a few genes. Oligogenic inheritance represents an intermediate between monogenic inheritance in which a trait is determined by a single causative gene, and polygenic inheritance, in which a trait is influenced by many genes and often environmental factors.
Mendelian traits behave according to the model of monogenic or simple gene inheritance in which one gene corresponds to one trait. Discrete traits with simple Mendelian inheritance patterns are relatively rare in nature, and many of the clearest examples in humans cause disorders. Discrete traits found in humans are common examples for teaching genetics.
Brachydactyly type D, also known as short thumb, stub thumb, or clubbed thumb, is a genetic trait clinically recognised by a thumb being relatively short and round with an accompanying wider nail bed. The distal phalanx of affected thumbs is approximately two-thirds the length of full-length thumbs. It is the most common type of brachydactyly, or shortness of digits, affecting approximately 2–3% of the population, and is associated with the HOXD13 gene, located on chromosome 2q31.1.
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