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Genetic Imprinting Definition
The inactivation of certain genes, determined by whether the gene is maternal (comes from the mother) or paternal (comes from the father). Genetic imprinting, also called genomic imprinting, appears to be another method of controlling genes by requiring one copy of each of certain chromosomes from each parent.
Inheritance patterns, which establish gene expression through dominance, regulate most gene expression and normally present paired chromosomes that determine which traits are expressed in the phenotype. However, it is possible for mutations to occur that result in both sets of a particular chromosome coming from the same parent (uniparental disomy). Though such mutations likely occur with no noticeable effect and thus remain undetected, they can allow rare recessive abnormalities to be expressed.
Though rare, the chromosomal disorders Prader-Willi syndrome and Angelman syndrome represent the most common pathology of genetic imprinting. These syndromes reflect uniparental disomy of chromosome 15, one of the chromosomes known to incorporate genetic imprinting. Chromosome 15 regulates numerous neurologic and musculoskeletal structures and functions that affect intelligence, cognition (the ability to think, reason, and remember), behavior, emotion, physical appearance, muscle tone, movement, and metabolism as well as reproductive health and capability.
Normal development requires one copy of chromosome 15 from each parent. When both copies of chromosome 15 are maternal (called paternal deletion), genetic imprinting produces a constellation of symptoms known as Prader-Willi syndrome. When both copies of chromosome 15 are paternal (called maternal deletion), genetic imprinting produces a constellation of symptoms known as Angelman syndrome. Each syndrome presents differing manifestations of neurologic dysfunction, musculoskeletal and other physical anomalies, and intellectual impairment.
Researchers believe genetic imprinting is a mechanism intended to prevent damaging mutations from propagating (extending themselves). Genetic imprinting appears to affect only certain chromosomes and, when it causes a disease state, results in related though differing symptoms, depending on the deletion.
See also CELL STRUCTURE AND FUNCTION.
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