Are all chimeric mice capable of transmitting the mutation though the germline?
No. Each chimeric mouse, even those created from the same ES cell clone and regardless of percent chimerism, is unique in its ability to transmit ES cell inherited genes. Germline transmission of ES cell derived genes in 129 derived chimeras mated to wild-type C57BL/6 is indicated by the production of agouti pups. It is not unusual for highly chimeric males (90-99% chimerism) to be sterile, or to produce many black pups before generating agouti pups. Some fertile males will never produce any agouti pups. In our experience, highly chimeric HM1-derived males often, but not always, generate agouti pups in the first or second generation. Agouti coat color only indicates the ability of the ES cell to give rise to germ cells and agouti pups must be genotyped for the inheritance of the mutated allele.
