From Chimera to Homozygous Null
(129 ES cells injected into C57BL/6 host blastocysts)
Chimeric mouse ♂ x C57BL/6 ♀ = B6129F1 and/or C57BL/6
B6129F1 coat color agouti, 50% carry targeted alleles +/-
B6129F1 ♂ +/- x B6129F1 ♀ +/- = B6129F2
B6129F2 coat color mixed, 25% homozygous -/- founders
B6129F2 ♂ -/- x B6129F2 ♀ -/- = B6129F3
B6129F3 coat color mixed, 100% homozygous -/-
B6129F3 are used for initially characterizing targeted genes