Dimples can be present on both cheeks or one, and some people have them on their chin. Like all physical traits that you possess you have two genes for them. One inherited from your father and one from your mother. The way that a physical trait is expressed, and hence the way you look is a result of either a combination of dominant genes, a dominant and a recessive gene or two recessive genes.
The genetics of dimples follows a dominant pattern of inheritance, that is to say that a child only needs to inherit one dominant gene for dimples to have them. When someone talks about a gene for dimples they mean a gene or set of genes that will produce the physiological and anatomical changes that result in these skin indentations. So what are the chances that a child may inherit them?

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If both parents have dimples then there's a 50-100% chance that their child will.
If the father has dimples and the mother does not, then the child has a 25-50% chance of inheriting dimples.
If the mother has dimples and the father does not, then the child has a 25-50% chance of inheriting dimples.
If both parents don't have dimples then their child will not, unless there is a spontaneous genetic mutation.