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Content: If one or both parents have a heritable disease, it may be passed down to a child. Genetic abnormalities may be passed down on dominant alleles (autosomal dominant inheritance) or recessive alleles (autosomal recessive inheritance). It is possible for a person to be a carrier of a disease but not have symptoms of the disease personally. This occurs when the disease is carried on a recessive allele. In other words, the trait cannot manifest in any person with a more dominant, healthy allele. If one parent is a carrier of a disease, while the other has two healthy alleles, the disease will not be manifested in any of their offspring. However, if bothparents are carriers, they have a 25% chance of having a child who is completely unaffected by the disease they both carry, a 50% chance of having a child who is also a carrier of the disease, and another 25% chance of having a child who suffers from the disease. Another way of looking at it is that any child they have has a 75% of being personallyunaffected by the disease. How diseases are inherited on the recessive allele. Image by the U.S. National Library of Medicine.