Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: David Cooper on 28/02/2014 17:37:18
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It's in the title - normal identical twins in that their main 46 chromosomes are identical, but with mitochondrial DNA from different sources. Would they still look near identical? Would they be equally good at running? Might one be fat and the other thin with identical diet and exercise? Have experiments been done on this in animals?
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I think they would look the same, unless one twin's mitochondria were out right genetically defective. There could be differences in metabolic rate, but you can also increase the number of mitochondria through aerobic exercise.
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If the twins are identical, they split from a single fertilised egg, with a single set of nuclear DNA.
However, the egg has numerous mitochondria, each with its own genetic code. When a cell divides, the mitochondria (http://en.wikipedia.org/wiki/Mitochondrion#Replication_and_inheritance) also divide, but may be unevenly partitioned between the daughter cells. This could result in a different genetic mix of mitochondria between the twins.
It is also possible that a new mitochondrial mutation could occur in one of the twins.
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I had never heard that every mitochondria has its own genetic code. In fact I thought that was the whole point of studying mitochondria DNA, that it was the same all the way down the maternal line except for mutations.
I have read about very rare instances of mitochondria from the sperm somehow getting into the egg.
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The idea was to have genetically altered identical twins (or clones) such that the only significant difference between them is the mitochondrial DNA (which would ordinarily be near identical too). What I really want to know is how much differences in mitochondrial DNA can contribute to differences between individual people, and this would obviously be easiest to test with modified clones, which means animal testing.
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Yes, clones as you described might be a good test, except that low oxygen stimulates mitochondria to reproduce and it might mitigate any differences.
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What I really want to know is how much differences in mitochondrial DNA can contribute to differences between individual people
Mitochondria generate the ATP which powers the cell. So the effects will probably be in anything which powers the cell metabolism - especially muscle, brain & eyes, which have especially high energy demands.
We can see the impacts of mitochondrial diseases (http://en.wikipedia.org/wiki/Mitochondrial_diseases#Characteristics); I imagine that mitochondrial function could affect activity and lethargy - but this will appear differently in different organs.
Many of the mitochondrial genes are actually expressed by DNA in the cell's nucleus (in humans, 13 proteins in the mitochondrial DNA, and approximately 1500 in the cell nucleus). I have heard that different species have quite different division of genes between their mitochondria and the cell nucleus.
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"Symptoms include poor growth, loss of muscle coordination, muscle weakness, visual problems, hearing problems, learning disabilities, heart disease, liver disease, kidney disease, gastrointestinal disorders, respiratory disorders, neurological problems, autonomic dysfunction and dementia."
That's quite a lot there that could potentially also be affected more subtly by small differences which aren't classed as diseases, but which could enhance or suppress athletic performance. The reason I'm thinking about all this is of course the fuss being made at the moment about children being born to three parents, where one supplies the mitochondrial DNA to prevent a mitochondrial disease being passed on by the "other" mother.