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Will mutations in mitochondrial DNA necessarily affect phenotypes?

I have some cursory knowledge of serial endosymbiotic cell theory, and find it difficult to consider that the DNA of the former cell — now organelle — would affect anything outside of the mitochondrion itself, although I can imagine the alteration of mitochondrial processes having an indirect effect on non-mitochondrial processes associated with certain phenotypes.

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  • $\begingroup$ I have edited your question slightly. It's best to make titles short and punchy and ensure that the body is self-contained (i.e. comprehensible without reference to the title). One thing I had difficulty with was your phrase "mitochondrial process as a catalyst for certain phenotypes". Catalyst means one thing in biochemistry, and this is not it. I have replaced it by "having an indirect effect". Is this what you meant? If not, try to phrase precisely what you do mean. $\endgroup$ – David Apr 29 at 13:20
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Assuming that I have understood (and reworded) the question correctly, I find the logic strange. It is the disruption of or change in process that produces phenotypic changes following a mutation in the gene, so if the process is critical for life — like those occurring in the mitochondrion are — what difference does it make where it is encoded?

Perhaps the problem is the endosymbiotic theory of mitochondrial origin. Yes, most of us believe that, but, whatever it was millions of years ago, the mitochondrion is an integral part of modern eukaryotes. Extensive changes have occurred, the most relevant to clearing up this way of thinking is the fact that most human mitochondrial genes are now encoded in the nucleus. Would you these genes would be any more or less likely to produce phenotypes on mutation? Hardly.

Now to the facts. There are certainly mutations in mitochondrial genes that are associated with disease in man and hence produce phenotypes. Some are listed in the table below, taken from a review by Taylor and Turnbull in 2004.

Clinical disorders that are caused by mutations in mitochondrial DNA

An account of Mitochondrial DNA and Mitochondrial Diseases written for less advanced audiences is this Scitable article.

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No, it will not necessarily affect phenotype. Of course silent or inconsequential mutations are possible in mtDNA just as they are in genomic DNA.

But, for example: In some cases, inherited changes in mitochondrial DNA can cause problems with growth, development, and function of the body’s systems. These mutations disrupt the mitochondria’s ability to generate energy efficiently for the cell.

(https://ghr.nlm.nih.gov/primer/mutationsanddisorders/mitochondrialconditions)

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