Based on this result, how many genes are represented by these mutants? A) 1 B) 2 C) 3 D) 4 (8) In generating knockout mice using embryonic stem cell procedure, what is the purpose of the double selections using NEO and TK genes? A) Making sure that homologous recombination occurs so that the wild-type gene can be replaced. B) Making the selection of transformants much easier C) Both A and B D) Neither