Cleft Chin and Genetics
The genetics of facial characteristics is a fascinating area and a cleft chin is actually caused by a dominant gene. This doesn't necessarily mean that if you happen to have a cleft chin, that all of your children will have this facial trait as well.
Every person inherits two sets of genes that determine the shape of their chin, one from each parent. Your partner's genetic makeup factors into whether your children have a cleft chin or a smooth one. If you and your partner have both inherited two cleft chin genes, the likelihood your children will have this trait is 100 percent.
However, just to confuse matters a touch it is likely that a cleft chin is not caused by one single gene; the version described above is an over simplification, often used in schools to explain how a physical characteristic is inherited. The truth is that there is probably a whole suite of genes that contribute to the formation of a cleft chin, although the genetic data on this is quite sparse. It may also be that environmental factors come into play as well and interact with those genes. These environmental factors can include the sub-cellular and extra-cellular environment around the genes, the uterine environment or indeed larger environmental factors that the mother's body is subject to.
In addition, if a person does have a dominant gene or genes for a cleft chin it does not necessarily follow that their child will inherit the facial characteristic and this can be due to variable penetrance. This phenomena is where a specific allele does not always produce its effect on the phenotype.