What have scientists found to be the most efficient and effective way to insert new sequences into an individual's DNA?

The current state-of-the-art method for editing DNA is based on CRISPR, which stands for "Clustered regularly interspaced short palindromic repeats."

While scientists have had the ability to tinker with DNA for decades now, it wasn't until just a few years ago that CRISPR allowed them to modify DNA in specific individuals with great precision and speed—and very low cost.

It's actually based on a defense mechanism certain bacteria evolved against viruses; in the bacteria it targeted specific sequences of virus DNA to destroy them, but we now use it to target specific sequences of any DNA and modify them.

CRISPR allows us to modify multiple genes at once, and do it all in a single generation—indeed a single individual if we want. Where previously we tried to haphazardly introduce genes heterozygously into mouse embryos and then bred them until we got what we want, now we just fire up the CRISPR and modify that specific gene in that specific mouse.

It also works on just about any species—indeed, there's no reason to think it wouldn't work on humans. This raises all sorts of ethical questions, however: Now that we have this amazing technology, how should we use it? What risks does it pose? Who should have access to it?