Final answer:
Polydactyly can be a family trait or part of a genetic syndrome, typically following dominant inheritance patterns. Though it's rare in the general population, it may be prevalent in isolated communities due to the founder effect.
Step-by-step explanation:
An extra digit, or polydactyly, may be a family trait, part of a genetic syndrome, or sometimes preserved. The condition is often seen as a Mendelian trait, following dominant inheritance patterns, but can also be part of more complex syndromes with multiple genetic factors at play.
In some cases, such as certain populations with a limited genetic pool, the incidence of polydactyly can increase due to the founder effect. One example is among the Amish populations, where a higher frequency of polydactyly has been observed. This is a result of genetic isolation and the presence of the gene in the initial small group of founders.
While polydactyly is a dominant trait, most people have five fingers because the gene for polydactyly is very rare in the human population and not all traits are determined by a single gene. In fact, most human traits, including things such as height, weight, and skin color, are polygenic—influenced by multiple genes adding complexity to inheritance patterns.