Mutations arise by random changes in our DNA. Although much of this damage gets repaired or eliminated at birth and thus does not get passed down to subsequent generations, some mutations called germ-line mutations can be passed town. Often times, these germ-line mutations are passed down with serious medical consequences to the offspring who inherit them. Founder mutations are the “long-gone” ancestors of a genetic legacy of mutations. As opposed to the victims of many genetic diseases who die before they can reproduce, founder mutations spare their carriers meaning that their mutations can be passed on or inherited by their offspring. These mutations give anthropologists a way to trace the history of human populations and their migrations around the world, which is why they serve as the footprints humanity has left in the trail of time. Founder mutations can be estimated by determining the length of the haplotype, which gets shorter over time. The original founder haplotype is actually the entire chromosome that includes the mutation. A young founder mutation should be able to be found in the midst of a long haplotype in people who have it today. An ancient founder mutation rests in a short haplotype in current carriers. Most founder mutations are recessive, so only a person with two copies of the affected gene (one from each parent) will suffer from the disease. The much larger percentage with only one copy are called carriers. They can pass on the gene to their children and have no symptoms of disease themselves, and the single copy of the founder mutation gives the carrier an advantage in the struggle for survival. Some examples include carriers of the hereditary hemochromatosis mutation. They are protected from iron deficiency anemia because the protein encoded by that mutated gene makes the person absorb iron more effectively than those who carry two normal copies of the gene. Someone who has two copies will probably die before reproducing, but those with only one copy will survive preferentially over those with no copies. This produces a balancing selection, in which the beneficial effects drive the frequency of the mutant gene up while the harmful effects damp down the frequency. Evolution gives and takes, so that over time the gene still maintains a relatively steady population level.

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