Debunking the Myth About Cleft Chin

Cleft chin: The myth Some people have a prominent dimple or crease in the front of the chin, called a cleft chin (or “butt chin“); others do not. This is sometimes said to be controlled by a single gene with two alleles, with cleft chin (C) dominant to smooth chin (S). The small amount of genetic data that is available shows that this myth is not true; in addition, there are many chins that are intermediate between clearly cleft and smooth. The frequency of cleft chin varies widely among different populations; Indian populations range from 4 to 71 percent cleft chin (Bhanu and Malhotra (1972). Günther (1939) recorded cleft chins in 9.6 percent of German men and 4.5 percent of German women. The large difference in frequency between men and women does not fit the simple genetic model of cleft chin being determined by a single autosomal (non-sex-linked) gene. Bhanu and Malhotra (1972) recorded the frequency of cleft chin in Indian boys and men of different ages. They said there was no difference in frequency of cleft chin among age groups, using a chi-square test, but when I analyze the data using logistic regression, I get a significant (P=) increase in cleft chin with age; about 5% of boys 6 to 10 years old have cleft chins, while 10% of men over 35 have a cleft chin. This change with age is also evidence against the simple genetic model. Family studies Lebow and Sawin (1941) first suggested that cleft chin was a genetic character, based on data from a single family. They suggested that cleft chin was recessive, although they admitted that they didn’t have definitive evidence. There is an unpublished dissertation by Pfannenstiel (1951), which I haven’t seen, that concludes that cleft chin is dominant, but affected by the environment (cited in Beckman et al. [1960]). Beckman et al. (1960) report the following data from Swedish families: Parents Cleft offspring Smooth offspring Percent cleft Cleft x Cleft 10 1 91% Cleft x Smooth 24 28 46% Smooth x Smooth 4 33 11% If the myth were true, two parents with smooth chins could not have a child with a cleft chin. While there is definitely a strong genetic influence, as parents with cleft chins have a higher proportion of cleft-chin offspring than do parents without cleft chins, the 4 cleft-chinned offspring from smooth X smooth parents do not fit the myth that cleft chin is determined by a dominant allele. Conclusion Many people have chins that are intermediate between clearly cleft and clearly smooth, and the family studies do not fit the myth that cleft chin is caused by a dominant allele. You should not use cleft chin to demonstrate basic genetics. References Beckman, L., J.A. Böök, and E. Lander. 1960. An evaluation of some anthropological traits used in paternity tests. Hereditas 46: 543-569. Bhanu, V., and K.C. Malhotra. 1972. A population genetic study of cleft chin in India. American Journal of Physical Anthropology 37: 367-372. Günther, H. 1939. Anomalien und Anomaliekomplexe in der Gegend des ersten Schlundbogens. Zeitschrift für menschliche Vererbungs- und Konstitutionslehre 23: 43-52. Lebow, M.R., and P.B. Sawin. 1941. Inheritance of human facial features: a pedigree study involving length of face, prominent ears and chin cleft. Journal of Heredity 32: 127-132. #chinDimple #chinCleft #cleftChin #dimpleOnChin #dimpledChin #dimplesOnTheCheeks #dimpleChin #freckles #hair #hairline #shapeOfFacialFeatures #UnderstandingGenetic #NikolaysGeneticsLessons #getRidOfCleftChinSubliminal #getRidOfCleftChinNaturally #getRidOfCleftChinWithoutSurgery #cleftChinRemovalSubliminal #cleftChinRemovalNaturally #cleftChinRemovalNonSurgical #cleftChinRemovalWithoutSurgery #removeCleftChinSubliminal #Genetics