Single-gene mutations are defects or changes in genes that may be passed on from generation to generation. The most common forms of inheritance include autosomal dominant, autosomal recessive, X-linked recessive, and new dominant mutations. Single-gene mutations may result in both structural and functional birth defects. These defects may be found in isolation or as part of a known syndrome and may display phenotypic variation, in which the same mutant gene leads to variable clinical problems. This often occurs with dominant mutations such as Marfan syndrome. A genetic disorder may also display reduced penetrance, wherein not everyone with the genetic mutation will have the disorder or trait. These are also known as "silent" disorders.
Adapted from "Leading Categories of Birth Defects." March of Dimes Perinatal Data Center, 2000.
a, a autosomal describes a chromosome other than the X and Y sex-determining chromosomes phenotypic related to the observable characteristics of an organism
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