MM6 wrote:one_irish_rover wrote:it is fascinating, cellular evolution. theory of endosymbiosis: basically a larger bacterium engulfed a smaller bacterium--thus was born the first eukaryotic cell (actually, it was proto-eukaryotic). More to it than that, like you said.
kudos to us for derailing yet another thread
Exactly ! clever clogs- is there anything I can say that you haven't heard of ??
MM6 wrote:there is a small stretch about 500 bases long called the control region which as you say does not carry any codes for anything. I was mistaken about fewer mutations - what I meant was the mutations are neutral in that they dont affect anything - but b/c this stretch of mtDNA is so short its much quicker to check - and cheaper. Thats where the syrian hamsters come in - Prof Sykes had to collect the mtDNA from these hamsters to prove that the mutations in the control region were not too frantic or erratic which would make it near impossible to distinguish important signals from the incidental irrelevant changes after a few generations.
one_irish_rover wrote:got it. but does Sykes say that mutations in the control region do not affect anything? bacause they do, more so than in protein coding regions, b/c the control region is cis-acting control element for many genes (gene networks). so, a mutuation in the control region could affect the expression of many proteins. does that make sense?
Are you confusing the nucleus DNA with the mt DNA control region? He says that b/c the mtDNA control region does not carry the codes for anything in particular the mutations dont affect the performance of the mt enzymes- however he counters by stating that it does sometimes happen when mutations hit other parts of the mt DNA outside the control region - he goes on to describe rare neurological diseases which are caused by the mutations in genes that disable essential parts of the mt machinery - but b/c they are so damaged they dont usually survive the next generation and so die out. The control region mutationms on the other hand are not eliminated precisely b/c the control region has no specific function. They are neutral. It appears that thsi stretch of DNA has to be there in order for mitochondria to divide properly.
one-irish-rover wrote:ok, i had to remind myself that the mt genome is much much smaller than the nuclear genome, and does not exist across dozens of chromosomes, so gene networks/orchestration is not as intricate, and so mt control region is relatively tolerant of high mutation rate. there are other difference between mtNA control region and control regions in nuclear DNA....blah blah, anyway i'm following you...
Exactly - you got it.
one_irish_rover wrote:i do. i'm not clear on how the mt control region of all these hamsters are identical. i'm going to have to think about that or you can explain it to me. the control region should differ between individuals (single nucleotide polymorphisms, at least). similar i can see, but exactly the same over thousands of years? moreover, if the control region is unimportant (as Sykes states) then this region should pick up many mutations and be passed on through generations, b/c they are meaningless, so there is no selection pressure. The thing is, they are meaningful, as I said up in that first paragraph. Mutations in control region are more meaningful than mutations in single genes, thus the control region is highly conserved across individuals (and across species). so, Sykes explained the control region incorrectly, it seems. i'm thinking out loud, i can't write all this. it's more for interactive realtime discussion.
I dont think he explained it incorrectly. The mtDNA is passed dwon directly from the female line. This means that there is little change in the mtDNA from generation to generation, unlike nuclear DNA which changes by 50% each generation. The fertilized egg contains a mixture of the father and mother's nuclear DNA and an exact copy of the mother's mtDNA, but none of the father's mtDNA. The result is that mtDNA is passed on only along the maternal line. This means that all of the mtDNA in the cells of a person's body are copies of his or her mother's mtDNA, and all of the mother's mtDNA is a copy of her mother's, and so on. No matter how far back you go, mtDNA is always inherited only from the mother. Even though everyone on Earth living today has inherited his or her mtDNA from one person who lived long ago, it says our mtDNA is not exactly alike. Random mutations have altered the genetic code over the millennia. But these mutations are organised, in a way. For example, say that 10,000 years after the most recent common ancestor, one of the mtDNA branches experienced a mutation. From that point on, that line of mtDNA would include that alteration. Another branch might experience a mutation in a different location. This alteration would also be passed on. What would eventually end up with are some descendants who have mtDNA that is exactly or very much like that of some people's, somewhat like that of others, and by looking at the similarities and differences of the mtDNA of all of these individuals, the researchers could try to reconstruct where the branching took place. hth.
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Perseverence..
Thank you. You're very nice.