|MadSci Network: Genetics|
Good question. There are actually two facets to your question, and I will answer them in turn. First, is the occurrence of birthmarks hereditary? Depends on the type of birthmark. There are several types of birthmark, generally named for what they look like. These include cafe au lait birthmarks, which are browner than the surrounding skin, red wine birthmarks which are red but smooth (like Mikhail Gorbachev's) and strawberry birthmarks, which are red and raised. Some rare hereditary conditions correlate with specific types of birthmark, but most birthmarks are sporadic. For example, people with the rare disorder neurofibromatosis usually have cafe au lait spots, but people with cafe au lait spots are unlikely to have neurofibromatosis. There are also hereditary syndromes where individuals are predisposed to have moles on their skin, but most people with moles do not have these syndromes. The second facet of your question is whether the location/shape of birthmarks is hereditary. In general the answer to this question is also negative: sporadic birthmarks generally represent a somatic mutation which occurred as an individual grew from an embryo. The affected region represents all the cells descended from the single cell where the mutation originally occurred. Thus, a mutation early in embryogenesis can affect a large area on a person's body, while a late mutation will affect a proportionately smaller area. However, because the mutation happened at random during development, the likelihood that any two individuals will have exactly the same birthmark is pretty small. Kind of like snowflakes. If you look at your birthmark and compare it with your father's, I will bet that you will find subtle but significant differences between them. Nonetheless, it is pretty cool that you've got a similarly placed/shaped birthmark. Just don't count on your kids having the same thing... Chris Carlson firstname.lastname@example.org
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