For a number of reasons, genetic mutations (changes to DNA) may or may not have an effect (or at least a noticeable one) (i.e. mutations may or may not be “silent”). It’s a lot more nuanced than whether or not it happens in a gene, and if it does whether it changes a protein letter (i.e. is non-synonymous) or doesn’t change a protein letter (is synonymous). Even those synonymous ones can alter translation rates and stability of the mRNA. There are also addition to possibilities for frame-shift mutations (that change all the protein letters after it) and nonsense mutations (which introduce a premature stop codon). And all of this has just been talking about the coding region (i.e. in the exons which have the protein-letter-adding-instructions). There can also be mutations in noncoding regions like introns and 5’ and 3’ untranslated regions (UTRs) that can affect how an mRNA recipe is processed and how well it’s used (are ribosomes now stalling on it or something?). Then there are changes outside of the gene, even far away from the itself that can impact its expression because DNA loops up and does all sorts of wild enhancer-y stuff to regulate expression.
A lot of time, when looking for disease-causing mutations, people look for nonsynonymous mutations in exons because those are most “obvious” sources of problems, but more and more research has shown the effects of other types of mutations on gene expression that can have big impacts. Don’t get scared, when we say “mutation” it sounds all scary, but really evolution is sculpted upon random mutations. And mutations in our germ cells (sperm & eggs) introduce important genetic variability. These changes, which we can also call “polymorphisms” which sounds less scary, help make you you!
There are, however, mutations that aren’t good, and this can cause diseases like cancer. But our bodies are usually really good at correcting the damage, and/or the mutations really are “silent.” When mutations happen in our somatic (non-germ line) cells, they only get passed onto cells made from those cells. So if they decrease a cell’s functioning those cells will probably just be a dead end. Mutations that increase a cell’s functioning too much can lead to tumor formation, etc. Basically everything is nuanced when it comes to mutations!
Including the terminology!
so here are links to posts where I cover some of it (today I just have time to talk it out):
genetic code basics: http://bit.ly/learngeneticcode
Ames test & difference between mutagen (can cause mutations) and carcinogen (can cause cancer) http://bit.ly/amestest