| Term | Definition |
|---|
| dynamic mutation | a phenomenon where the onset of symptoms of a hereditary disease appears to occur at a progressively earlier ages in successive generations withing a particular lineage |
| trinucleotide repeat expansion mutations | stem from expansion of trinucleotide repeats (CAG)n or minisatellite DNA regions located within genes or regulatory regions of genes |
| anticipation | the larger the repeat, the earlier the onset of disease |
| pre-mutation | an intermediate level of repeat-expansion, often asymptomatic |
| triplet repeat expansion disorders | large expansions associated with altered DNA methylation and loss of gene function (ex. fragile X) |
| Fragile X | most common cause of inherited mental retardation in males, hyperactivity, autistic features, ADD, narrow face with prominent forehead, jaw, and ears; macroorchidism, folate-sensitive site at Xq27.3 |
| Huntington Disease | dominantly inherited, progressive brain disorder, causes mental and physical deterioration, death within 15-20 years after onset of symptoms, caused by an excess of CAG repeats |
| Uniparental Disomy | when a child inherits two copies of a chromosome from one parent and none from the other parent, can be caused by trisomic rescue, monosomic rescue, or gamete complementation |
| heterodisomy | inheritance of 2 homologous chromosomes from one parent with different genetic content |
| isodisomy | two identical copies of a single chromosome |
| genomic imprinting | we inherit 2 copies of our autosomal genes from our parents and sometimes only one copy is active |
| epigenetic | trait affecting gene expression that is hertiable through cell divisions, but that does not involve alteration in the primary DNA sequence |
| imprinting | an epigentic marking of a gene based on its parental origin |
| paternal imprinting | phenotypic effects of an allele are not expressed when inherited from father |
| maternal imprinting | phenotypic effects of an allele are not expressed when inherited from mother |
| Prader-Willi | characterized by uncontrolled eating, small hands and feet, short stature, hypogonadism, mental retardation and behavior problems in adults, caused by deletion of chromo 15 or maternal uniparental disomy for chromo 15, or a mutation involving imprinting |
| Angelman syndrome | characterized by severe mental retardation, speech impairment, unsteady gait and/or tremulousness of the limbs, also present with inappropriate laughter and excitablitity, its caused by deletions of materneral chromo 15, paternal uniparental disomy for chomro 15, or an imprinting defect |
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