Genetic Traits: Dimples

I still remember the day when my little one smiled for the very first time. Joe, my baby-boy looked at me and smiled the cutest smile in the world. Greg, my husband, and me marveled at the wonders of nature when we realized that Joe’s smile completely resembled mine! Yes, even he had a dimple on both his cheeks! That was when Greg said to me, "I love you, but not more than our little one!" Tears rolled down my cheeks, into my dimples as I smiled and cried at the same time…I didn’t know what was happening to me. - A page from the diary of Jane, a dear friend.

Technically speaking, dimples are visible indentations formed as a result of the underlying flesh of the cheeks. It is hard to believe that dimples are actually the manifestations of a birth defect resulting from a shortened facial muscle. A dimple is the outcome of a fault in the subcutaneous connective tissue that develops during embryonic development. Also, a variation in the structure of the facial muscle zygomaticus major is known to cause dimples. When a person smiles, the shorter muscles on his/her face cause the facial skin to get pulled, thus creating a slight depression in the skin, a dimple. A pull in the skin of a person’s chin caused by a shortened chin muscle, results in a dimpled chin. And that reminds me of the very famous rhyme, "chubby cheeks, dimple chin…"

How is dimple formation related to genetics? Well! Dimples are a dominant genetic trait and are inherited from one generation to another. Dimples on both cheeks are a common occurrence, while a single dimple that occurs on one side of the face is a relatively rarer phenomenon. As dimples are a dominant trait, only one gene is required to inherit dimples.

The sex cells created through meiosis prior to the process of reproduction, can contain genes that produce dimples or genes that produce the muscles controlling dimples. During reproduction, each parent provides one of these genes to the child. Since the dimple gene is dominant; a child has dimples, if the gene is present in him/her. It means that if both your parents have dimples, you have 50-100% chances of inheriting dimple genes. If one of the parents has dimples, there are 50% chances that their children will have dimples. If both the parents do not have dimples, there are no chances that their children will have them. However, their children can pass recessive dimple genes to future generations. Dimples can be passed through multiple generations of a family.

Penetrance is defined as the frequency with which a heritable trait is manifested in individuals carrying the genes conditioning it. A variation in penetrance is referred to as variable penetrance. On account of this phenomenon, some individuals are only carriers of a particular gene but do not exhibit the traits associated with it. However, they function as carriers of the gene and pass the traits to their successive generations.

In some cases, dimples can result from spontaneous mutations. In such cases, a slight defect in the facial muscles causes a dent in the cheek or a cleft chin, thus resulting in the production of dimples. Reduced penetrance is a phenomenon whereby certain genetic traits skip some generations and reappear in subsequent generations in varying genetic patterns. At times, it so happens that a person inherits a certain genetic trait and also inherits another trait that suppresses the prior one. For example, if a person inherits the genes for dimples but also inherits the genes responsible for a small face, the dent in the person’s facial muscles will not be apparent on account of the reduced size of his/her face. The person functions as a passive carrier of the genes for dimples in such cases as well.

Strangely, dimples, which are believed to beautify your face, are actually defects in your facial muscles. They are a classic example of the adage that says, "Imperfection is beauty!"