The following document outlines the genotyping strategies for detecting tm1a conversion to the b, c and d forms
After treatment with a source of Cre recombinase to excise the critical exon and neo cassette (in promoter-driven lines), the Tm1a allele is converted to the Tm1b form. After treatment with a source of Flp recombinase to excise the selection cassette, the Tm1a allele is converted to the Tm1c form.
Please see the PDF attached for more information.