Normally, genes are expressed from both the maternal and the paternal allele. Genomic imprinting results in allele-specific expression of certain genes from either the paternal or the maternal allele. These genes are marked before fertilization in a way that either the maternal or the paternal allele is transcriptionally silenced in the offspring. One of the first indications that certain autosomal regions are subject to genomic imprinting came from mouse genetic studies using Robertsonian and reciprocal translocations. In these studies, uniparental duplications or deficiencies for certain chromosomal regions were analyzed. The failure of a disomy or duplication from one parent to complement a corresponding nullisomy or deficiency from the...