The ability to replace the wildtype alleles with a knockout allele in mice has enabled researchers to carry out important reverse genetics studies on gene function. Please select all of the statements below which correctly describe the creation of gene knockout mice. Multiple answers are possible, and partial credit will be given.

A. Homologous recombinants of the knockout alleles are desired since they will replace the wildtype allele.

B. Resistance to the anti-viral drug ganciclovir indicates that homologous recombination has occured.

C. The embryonic stem cells carrying homologous recombinants of the knockout allele are placed back into a blastocyst and injected into a surrogate mother to produce mice carrying the knockout allele.

D. Illegitimate recombinants have the knockout allele randomly inserted and do not replace the wildtype alleles and may potentially insert into other genes and confound the analysis.

E. Resistance to neomycin indicates insertion of the knockout allele but does not distinguish between homologous and non-homologous recombinants.