The terms cleft chin,chin cleft,dimple chin, or a chin dimple refer to a dimple on the chin. It is a Y-shaped fissure on the chin with an underlying bony peculiarity.[clarification needed] The chin fissure follows the fissure in the lower jaw bone resulted from the incomplete fusion of the left and right halves of the jaw bone, or muscle, during the embryonal and fetal development. For other individuals, it can develop over time, often because one half of the jaw is longer than the other, leading to facial asymmetry.
This is an inherited trait in humans, where the dominant gene causes the cleft chin while the recessive genotype presents without a cleft. However, it is also a classic example for variable penetrance with environmental factors or a modifier gene possibly affecting the phenotypical expression of the actual genotype. Cleft chins are predominant among people of Germanic and West Slavic (i.e., Polish) ethnicity. It is very common in that part of the world and among descendants of people originating in that part of Europe.
^Günther, H. 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. Inheritance of human facial features: a pedigree study involving length of face, prominent ears and chin cleft. Journal of Heredity 32: 127-132.