Fmr1^tm1Usdn

The (CGG)6 repeats in exon 1 were replaced with two different Sfi 1 sites and these sites were used to insert a premutation-sized repeat tract that was generated by serial ligation of short, stable CGG.GCC-repeat. In addition a 38LoxP vector containing a loxP flanked neomycin resistance cassette was inserted into intron 1. Crossing with mice expressing cre in the germline removed the neo cassette. These mice contain large repeat expansions that transform a premutation-sized allele into a full mutation sized allele in a single generation. (J:121413)