Prader-Willi syndrome and Angelman syndrome are distinct genetic disorders caused by the same deletion on human chromosome 15. The resulting phenotype depends on whether the deletion is inherited from the father (Prader-Willi) or the mother (Angelman). This differential expression of a gene based on its parental origin is an example of:
- Sex-linked inheritance
- Mitochondrial inheritance
- Genomic imprinting (correct answer)
- Pleiotropy
Explanation: Genomic imprinting is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner. In this case, genes in the critical region on chromosome 15 are 'imprinted' or silenced in either the egg or the sperm. Consequently, the zygote has only one active copy. If the active copy inherited from the father is deleted, Prader-Willi syndrome results. If the active copy inherited from the mother is deleted, Angelman syndrome results. This is a classic example of imprinting, a non-Mendelian effect.