Mouse GABA A receptor beta 3 subunit gene (Gabrb3) is located at the imprinted region on chromosome 7. To detect a possible biased parental expression from Gabrb3 gene, a dimorphic PstI restriction enzyme site was used for restriction fragment length polymorphism (RFLP) analysis. RFLP analysis of PCR-amplified Gabrb3 cDNA from brain tissue of hybrid mice proved that Gabrb3 gene is not imprinted. Quantitative analysis of allelic expression of Gabrb3 showed that DBA/2 allele was more expressed than C57BL/6 allele in (C57BL/6 × DBA/2)F1 and (DBA/2 × C57BL/6)F1 hybrid mice indicating that Gabrb3 gene expression is influenced by strain-of-origin rather than by parent-of-origin For discrimination and quantitation of transcripts from homologous alleles without RFLP, allele specific termination (AST) analysis was developed. Control experiments with GABA A receptor gamma 2 subunit gene (Gabrg2) proved that AST analysis is highly sensitive for the minor allele transcript representing over 10% of total transcripts of a gene. Application of AST analysis revealed that Fas gene is equally expressed from both parental alleles in (C57BL/6 × BALB/C)F1 hybrid mouse.