A minigene containing the coding sequence of the inserted gene was coupled to genomic sequence containing the last three exons (3' part of exon 9 through entire exon 11) of the host gene. This combined sequence followed by a loxP-flanked neomycin resistance gene cassette was inserted at the ATG translation start site of the host gene. This allele was used as a hypomorph because the still present neo cassette attenuates the expression of the inserted gene. (J:234164)