Assays to determine allelic usage of gene expression in the placenta

Mammalian placentas express a large number of so-called imprinted genes. Imprinting refers to mono-allelic or biased expression based on which parent contributed the allele. Many of these imprinted loci encode factors involved in growth and cell-cycle regulation, as well as maternal behavior. In general, paternally expressed genes tend to enhance growth, whereas maternally expressed genes inhibit growth. Methods are described for developing assays to test the allelic usage of a gene. The approaches described are best utilized within a system where multiple strains are available, and it is possible to perform reciprocal crosses. Only polymerase chain reaction-based methods are examined in any detail.