Hello. Is it possible that a deletion can occur in the middle of only one strand of a human autosomal chromosome?
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4$\begingroup$ When people say "strand" in DNA, they refer to one sugar-phosphate backbone with one series of nucleotides. DNA is typically double stranded and RNA is typically single stranded. But when you talk about a "chromosome pair", you're not talking about a pair of strands, you're talking about a pair of chromosomes. Each chromosome is double-stranded. So, what do you actually mean in your question? $\endgroup$– Bryan Krause ♦Commented Dec 22, 2023 at 14:00
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$\begingroup$ I have altered the question title from "Can a deletion occur on only one strand of a human chromosome pair?" by deleting the word "pair". This matches the version of the question in the body and makes the most sense as a question. It is also the question that had been addressed by the two answers that had been posted at the time I made the change. $\endgroup$– mgkrebbsCommented Dec 22, 2023 at 17:27
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2 Answers
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This is a somewhat semantic question. In terms of WHEN a deletion happens, I think it's commonly on only one strand as most mutations are caused by a collision from radiation or sometimes a chemical. That will typically only affect one base. BUT there are repair mechanisms that come in and can cause a deletion on both strands or repair the damage. In the long term the repair mechanisms work pretty hard to make sure both strands are the same in the end.
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As it appears that most deletions occur by mechanisms that do not involve large-scale strand separation (e.g. during crossing over or by translocation etc.) this is unlikely to happen (see e.g. Wikipedia article). These vary in length from perhpas a dozen base pairs to thousands or more, and differ from mutations caused by radiation and chemicals. Any small deletions on one strand (e.g. at single-strand breaks) need to be filled in if replication is to occur.