Measuring is an absolutely fascinating procedure. The predominant method is called sequencing by synthesis. Illumina is the company that basically rules the market for this technology, they have some decent explanatory videos if you’re interested.
The first steps are to isolate DNA, then break it into small bits, replicate those small pieces thousands of times, and then anchor these to a glass slide. Then flow a solution over the slide with the individual DNA bases (ATCG) that have been modified to fluoresce when illuminated with a certain wavelength of light. These fluorescently labeled nucleotides get assembled one by one into strands that match the small fragments from the DNA sample. Each time the fluorescent DNA bases are added a laser is shined on the glass slide and a very sensitive microscope camera reads how many strands shone at the frequency that corresponds to A T C and G. This tells you which base just got added to which strand. Repeat a couple hundred times and you have a huge number of sequences of ATCG’s corresponding to each short strand of DNA in the sample.
The problem now is assembling these short sequences into a full genome. Basically, the puzzle is finding the arrangement of short sequences that maximizes the overlap between them and their agreement with a reference genome. It’s a pretty interesting problem that (I believe) is classically solved with dynamic programming, although I don’t know the most recent methods.
I really don’t think it’s well enough appreciated how integral computation is to DNA sequencing. Signal processing in the camera, assembling the genome fragments, determining whether a mutation exists, and all the subsequent analysis to give biological meaning to a sequence.
This is the kind of content I visit this site for.
This formulation has the added benefit of not being easily answered with a flippant remark.
Don't take the chance, people. Edit your DNA with notepad.
We have a set of tools that let you determine biological structures (sometimes entirely, sometimes only partially).
We also have a set of tools to modify genes. Some viruses already do this, so we use them. Were also using CRISPR which is based on the machinery of bacteria.
So you use the modification tools to change genes and the analytical tools to prove you did it correctly.
Of course the level of complexity is way higher since your dealing with a living organism and the modification tools (and analytical tools) aren't perfect, so there is a ton of trial and error to do to correctly.
Like, it is very, very small thing. How do you even measure it, let alone replace it?