This was often NOT done in many transgenic experiments 20 to 30 years ago. In mice transgenic insertions and inadvertent disruption of genes near the transgene

This was often NOT done in many transgenic experiments 20 to 30 years ago. In mice transgenic insertions and inadvertent disruption of genes near the transgene insertion are only occasionally disruptive. The reelin gene disruption is a good example. This work was started long before cheap whole genome sequencing. However, comments are right—it was never too hard to examine the flanking sequence around the insertion site. Just offered to help the team with telomere-to-telomere of the few rare wild American chestnut survivors. There are not that many.