Dimples are small, natural indentations on the skin, most commonly observed on the cheeks. They typically become apparent when a person smiles. They are formed due to a variation in the underlying facial muscle structure, specifically the zygomaticus major muscle. This muscle, which helps in raising the corners of the mouth during a smile, can sometimes divide into two separate bundles, creating a slight depression in the skin.
The Genetics of Dimples
The presence of dimples is widely considered a genetic trait, often inherited within families. While research into the specific genes involved is still developing, dimples are generally categorized as an autosomal dominant trait. This means an individual typically needs to inherit only one copy of the gene responsible for dimples from either parent to exhibit the trait. The gene believed to influence cheek dimple formation is thought to be located on chromosome 5.
Genetic inheritance, however, is not always straightforward. Although dimples are classified as dominant, their inheritance pattern is often described as “irregular dominant” due to its unpredictable expression. This suggests that while a single gene may largely control the trait, multiple other genes can also influence whether dimples appear and how prominently. If one parent has the gene for dimples, their child generally has a 50% chance of inheriting the trait. When both parents possess dimples, the likelihood of their children inheriting them can range from 50% to 100%. Based on classical Mendelian genetics, if neither parent carries the gene for dimples, their children would not typically develop them.
Why a Child Might Have Dimples When Parents Don’t
Despite the general principles of dominant inheritance, it is possible for a child to have dimples even if neither parent visibly exhibits them. One explanation involves a concept known as incomplete or reduced penetrance. This occurs when an individual carries the gene for a particular trait, such as dimples, but does not physically express it themselves. They can still pass the unexpressed gene to their offspring.
Another factor contributing to this phenomenon is variable expressivity. A parent might possess the dimple gene, but their dimples could be very subtle or faint, making them difficult to notice. In such cases, the child might inherit the same gene, but express it more strongly, resulting in clearly visible dimples.
In rarer instances, a child may develop dimples due to a spontaneous genetic variation or mutation. This means a new genetic change occurs that was not present in either parent, leading to the development of the trait. The complex interplay of multiple genes, along with these genetic phenomena, contributes to the nuanced and sometimes unexpected inheritance patterns of dimples.