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Founder mutations are a class of disease-causing genetic mutations, each derived from its own ancestral "founder" in whom the mutation originated. While most disease-causing mutations are found in humans at a rate of one in a few thousand to one in a few million people, founder mutation can occur at much higher rates. This apparent anomaly is partially explained by the fact that most founder mutations are recessive: only a person with copies of the affected gene from both parents becomes ill. Most people with only one copy of the gene-"carriers"-survive and pass the gene to offspring. Furthermore, the single copy of a founder mutation often confers a survival advantage on carriers. For example, the hereditary hemochromatosis mutation protects carriers from iron-deficiency anemia because the mutated gene allows increased efficiency of iron absorption.