An animation describing how some traits and diseases have different frequencies in different populations, based on the history of genetic mutations, migration patterns, and cultural influences.

From a genetic point of view, a population is a group of people that share common genetic ancestry (shown as groups of dots), including mutations that have accumulated over time (red and orange dots). Much of this genetic variation arose in prehistoric times, when people lived in small, isolated communities. Some mutations produced new traits that provided advantages in new environments; some caused diseases. Some genetic variation can be lost when a subgroup of a population migrates to a new home – taking only some of the accumulated mutations. The founders of the new population may, by chance, carry with them one or more rare mutations. This is called the “founder effect.” Over generations, there is an increased chance that breeding among the small number of migrants will increase the prevalence of these mutations. Recently, people have become more mobile and cities have become multiracial. Even so, there are still regions of the world where people are born, reproduce and die within a small area. These populations preserve their distinct genetic character through generations of isolation, both geographic and cultural. The Amish people of North America provide a classic example of the founder effect. In the 18th century, about 200 Amish people from Europe founded communities in Pennsylvania, Indiana and Ohio. The Amish maintained their distinct religion and culture. Inbreeding produced a higher prevalence of several genetic traits and diseases, notably dwarfism and maple syrup urine disease. Ashkenazi Jews also have increased prevalence of several genetic diseases. There were multiple founder effects during millennia of migrations (diasporas). Each community remained relatively distinct from its surrounding culture. In recent generations, Jews have increasingly assimilated into many populations. With non-religious (secular) upbringing and marriage to non-Jews (Gentiles), people may “forget” their Ashkenazi Jewish genetic ancestry. However, they are still at higher risk of being a “carrier” for certain genetic diseases.

population, mutation, genetics, carrier, DNA, migration, bottle neck, founder effect, Amish, Jewish, Ashkenazi, screening