Hbb-b1 and Hbb-b2 were replaced with sequence encoding human HBB containing the beta-thalassemia associated mutation, IVS-2-654. The insertion was made using the "plug and socket" method which leaves an hprt gene downstream of the inserted human sequence. RT-PCR analysis of heterozygous mutant mice identified aberrant splicing similar to that observed in humans with the IVS-2-654 mutation. (J:64295)