This article rings so true to me. My father is a microbiologist - and now, so is my fiancée. I'm very lucky that I get to learn about genetics through osmosis now, and boy, is it ever fascinating!<p>I had a dining-table discussion with my dad the other day where the subject of DNA mismatch repair came up. It turns out that, in E. coli, a very simple & widely studied prokaryote, there's a mechanism called DNA mismatch repair which fixes errors which might occur during DNA copying. If an error is detected - a mismatch (e.g. a G paired with a T) - a trio of proteins (MutL, MutS, MutH) spring into action. The original template strand is already methylated - marked with an extra methyl group - at certain points in the genome (usually where there's a C followed by a G). The daughter strand, on the other hand, is usually not methylated yet. So, one of these proteins starts running down the DNA from the mismatch site, looking for a methyl group - up to 1000 base pairs away. When it finds a site with a methyl group on one side but not the other, it nicks (marks) the daughter strand, and another protein complex comes along and chops up everything from the nick to the mismatch site. The DNA polymerase then comes by and resynthesizes the whole strand.<p>Just three proteins are needed to drive this complex algorithm - a linear search procedure which distinguishes the mother from the daughter strand, a marking procedure which identifies the incision point, and a third to chop up the DNA and prepare it for resynthesis. What's even more bonkers is that E. coli - under stressful situations - will disable certain DNA repair mechanisms to deliberately induce more mutations. And I know that there are thousands more such pathways and complex interactions going on in cells all the time - many of which we simply haven't discovered or probed yet.<p>I wish that everything in biology could be explained so neatly. Unfortunately, real biology is so incredibly messy. There's just so much we don't know - and so much that we can't neatly slot into an explanation like this. But, I know now that in another life I probably would have been a biologist!