Missense mutations at codons 207 and 208 were introduced at the endogenous locus via homologous recombination. The mutations were designed to substitute a glutamate (207) and glycine (208) with alanine residues. A floxed neo cassette was integrated upstream in intron 2 for selection. Mice carrying this allele were used to generate Esr1tm1.1Lja. (J:79228)