Cleft Chin
What Do Classrooms Say?
Classrooms teach that chins can be divided into two clear categories, cleft chins and non-cleft chins. Cleft chins are those that have a prominent dimple or crease in the front of the chin. Regular chins are smooth and do not have this dimple. According to textbooks, cleft chins (C) are the dominant trait while attached smooth chins are the recessive trait (S). |
What Do Classrooms Say?
Classrooms teach that chins can be divided into two clear categories, cleft chins and non-cleft chins. Cleft chins are those that have a prominent dimple or crease in the front of the chin. Regular chins are smooth and do not have this dimple. According to textbooks, cleft chins (C) are the dominant trait while attached smooth chins are the recessive trait (S).
What Does the Research Say?
Parents Cleft offspring Smooth offspring Percent Cleft
CxC 10 1 91%
CxS 24 28 46%
SxS 4 33 11%
3. McDonald (2011) analyzed the data of cleft chin frequency among Indian boys and men of different ages. His data suggests a significant increase in cleft chins with age. About 5% of boys 6 to 10 years old have cleft chins while 10% of men over 35 years have a cleft chin.
Conclusion:
Chins cannot be divided into just two categories: "cleft chin" and "not cleft chin". From the picture below it's clear that there is a whole spectrum of chins between the two categories. There is a whole range of chins between the clearly cleft and the clearly smooth. While there is probably some genetic influence on cleft chin, the family studies above show that it does not fit the simple one-locus, two-allele myth.
Classrooms teach that chins can be divided into two clear categories, cleft chins and non-cleft chins. Cleft chins are those that have a prominent dimple or crease in the front of the chin. Regular chins are smooth and do not have this dimple. According to textbooks, cleft chins (C) are the dominant trait while attached smooth chins are the recessive trait (S).
What Does the Research Say?
- Lebow and Sawin (1941) first suggested that the cleft chin was a genetic character based on data from a single family. Contrary to what classrooms teach today, they suggested that the cleft chin was a recessive trait.
- Beckman (1951) concludes that the cleft chin is dominant but affected by the environment. The following is the data they collected after looking into 100 Swedish families:
Parents Cleft offspring Smooth offspring Percent Cleft
CxC 10 1 91%
CxS 24 28 46%
SxS 4 33 11%
3. McDonald (2011) analyzed the data of cleft chin frequency among Indian boys and men of different ages. His data suggests a significant increase in cleft chins with age. About 5% of boys 6 to 10 years old have cleft chins while 10% of men over 35 years have a cleft chin.
Conclusion:
Chins cannot be divided into just two categories: "cleft chin" and "not cleft chin". From the picture below it's clear that there is a whole spectrum of chins between the two categories. There is a whole range of chins between the clearly cleft and the clearly smooth. While there is probably some genetic influence on cleft chin, the family studies above show that it does not fit the simple one-locus, two-allele myth.
Sources:
Beckman, L., J.A. Böök, and E. Lander. 1960. An evaluation of some anthropological traits used in paternity tests. Hereditas 46: 543-569.
Jones, Kristin. "Genetics Unit." Biology Class. Novi High School, Novi. 8 Dec. 2010. Lecture.
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.
McDonald, John H. "Myths of Human Genetics." : Cleft Chin. University of Delaware, 29 Oct. 2012. Web. 18 Jan. 2014.
Beckman, L., J.A. Böök, and E. Lander. 1960. An evaluation of some anthropological traits used in paternity tests. Hereditas 46: 543-569.
Jones, Kristin. "Genetics Unit." Biology Class. Novi High School, Novi. 8 Dec. 2010. Lecture.
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.
McDonald, John H. "Myths of Human Genetics." : Cleft Chin. University of Delaware, 29 Oct. 2012. Web. 18 Jan. 2014.