You have worked on a gene for eternal youth for the past ten years and discovered it is not the needed expression of a gene at all but the presence of an ""old age"" gene that needs to be knocked out to get to the ""fountain of youth."" what would be the outcome if the procedure used to make the gene-targeted (knock-out) mouse for the foy (fountain of youth knock out mouse) was embryonic lethal? would this still be a useful model to study?