Prader-willi syndrome is a genetic disorder involving a partial deletion of chromosome 15q on the paternal chromosome. when both copies of a gene (or chromosome) are functional but only one is expressed, this is an example of

position effect variegation

chromatin modifications

histone acetylation

genomic imprinting

x-inactivation

genomic imprinting

Explanation:

Genomic imprinting is a mechanism for regulating gene expression that allows expression of only one of the parental alleles, although both alleles are functional. Unlike most genes in which expression is biallelic, genes that are subjected to this mechanism (imprinted genes) have monoalelic expression; By definition, in an imprinted loci, only one allele is active (maternal or paternal), and the inactive is epigenetically marked by histonic modification and / or methylation of cytosines.

Genomic imprinting can cause some disturbances, among them Prader-Willi syndrome, which is a genetic disorder that involves a partial deletion of chromosome 15q on the paternal chromosome.

multiply it by 5 in order for you to understand i cant give an exact answer.