The region containing Mir34b and Mir34c was flanked by loxP sites. The distal LoxP site was inserted into a non-conserved region approx. 400 bp downstream of Mir34c. A positive selection cassette (NeoR) was flanked by FRT recombination sites and co-inserted with the proximal LoxP site into non-conserved regions approx. 800 bp upstream of Mir34b sequence. The conditional allele was obtained after Flp-mediated removal of the selection marker. Cre-mediated recombination removed the microRNA cluster. (J:147112)