Mir29b2 and Mir29c in this microRNA cluster were replaced via homologous recombination with a puromycin/thymidine kinase fusion gene under the control of EM7/PGK promoters. The inserted selection cassette was flanked by loxP and F3/FRT sites. Cre-mediated recombination excised the replacement cassette. (J:174268, J:267719)