To elaborate on the title: Among somatic, post-mitotic cells, would the same intron on a given chromosome have the same sequence among all cells descended from a progenitor cell?
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$\begingroup$ Welcome to SE Biology! See here for some advice on ways to ask questions that are likely to get a helpful answer. Have you looked at any examples of introns on the same chromosome? Can you cite any sources suggesting what you ask is the case? $\endgroup$– Maximilian PressMar 29, 2022 at 23:23
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$\begingroup$ Hi I'm just asking out of curiosity. Not sure how, if I got a sequence, I would know whether that would be the same for each cell in a sample, given that genomes are assembled from several reads and sometimes individual bases are averaged, right? Just off the top of my head, I figured that since introns are not coding for proteins but do regulate gene expression, there would be less of a force for their sequence conservation between divisions from a stem-like progenitor, but that's why I'm asking. $\endgroup$– UD22022Mar 30, 2022 at 1:49
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1$\begingroup$ Could you perhaps edit your query to include those details with any appropriate references as comments are ephemeral in nature and we want to questions to be self-contained and last over time. Please also take our tour and refer to the help center for guidance as to our ways. $\endgroup$– Jiminy Cricket.Mar 30, 2022 at 17:42
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$\begingroup$ I think that ignoring genome assembly for now may clarify the issue. I still don't understand the question. Are you referring to the same intron across different cells, or different introns on the same chromosome? Your comment makes it sound like the first, but your question makes it sound like the second. $\endgroup$– Maximilian PressMar 30, 2022 at 20:55
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1$\begingroup$ Sorry for being unclear. I meant the same intron, on the same chromosome, in different cells. Also changed the question to reflect this. $\endgroup$– UD22022Mar 31, 2022 at 2:34
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1 Answer
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I believe that the kind of mutation that you are interested in is somatic mutation, as opposed to germ-line mutation.
Any given genomic locus (intron, exon, intergenic region) probably doesn't mutate most of the time. In the case of somatic mutation, it is yet more likely that no mutation happens.
Nonetheless, such mutations do happen, in all of those different regions. For example, here is a study that catalogs somatic mutations in introns that lead to a particular phenomenon called intronic polyadenylation; here is another that catalogs intronic mutations that mess up splicing.
The same is true for protein-coding somatic mutations, one can find similar catalogs of mutations for those.
Such mutations in different regions (intronic, exonic, and otherwise) are all of interest as events that can lead to cancer.
None of this should distract us from that fact that usually mutations don't happen at any given site. But it's a question of probabilities, not of absolutes.
answered Mar 31, 2022 at 4:11
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$\begingroup$ OK humor me this. What if you were trying to engineer, using some DNA editing technology, several cells in a sample at once, and wanted to precisely introduce a double-stranded break at some intronic site. Would the risk of somatic mutation ever be a concern? Thanks $\endgroup$– UD22022Mar 31, 2022 at 11:12
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$\begingroup$ @UD22022 Somatic mutation is always a possibility. But, frankly, the efficiency of gene editing technologies is (at a guess) a 2-3 orders of magnitude higher than the rate of somatic mutation. You could not exclude the possibility without recovering and analyzing the edited cells. But you generally have to isolate, select, and culture edited cells anyways. I would say that it is a theoretical concern worth keeping in mind examining data, but likely not a regular practical concern for gene editing compared to e.g. the rate of off-target effects of editing. $\endgroup$ Mar 31, 2022 at 22:19