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Dolly the Sheep not totally identical clone
Marillion writes "Dolly, the first animal cloned from an adult mammal
has variances in her DNA from her "Mother." " The variances in the DNA are actually in the mtDNA, or mitochondrial DNA. It's an interesting read if you are interested in cell biology/embryology.
This result was not wholly unexpected - in fact it would have been a much bigger surprise if Dolly had managed to hang on to the mitochondrial DNA of her "nuclear" mother. The technique used here was to extract the nuclear DNA and from one cell and stick it into an egg cell which had its original nuclear DNA removed. Mitochondria live outside the cell nucleus and have their own, cut down, DNA genomes. In fact they're really bacteria that invaded, and became symbiotic with, our cellular ancestors about 1.1 billion years ago. We're all mosaic creatures... In any case before people start making speculations about human cloning please note cloning is amazingly unreliable, Dolly was 1 success out of about 200 attempts. Nobody's really improved on that success rate despite all the goats, mice and cows we've seen cloned. Imagine needing 200 pregancies to guarantee one healthy child in a ninth month period and you'll see why human cloning is a ways off.
Some background:
Mitochondria are cellular components that produce energy for the cell. The best scientific guess on their origin is that they were one invasive bacteria, but they enhanced some cellular function and evolved into a symbiotic role within the cell.
As decendants of cells, they carry their own unique DNA and RNA sequences. Their DNA data set is much smaller than that of the host cell, mutates at a slower rate, and is only passed down the female line. The scientists are running into the part of the mitochondrial mechanism that ensures that mtDNA is passed along the female line. Simply, the mitochondria of the host egg are more numerous and better equipped to deal with intruding foreign mitochondria. It will only be a matter of time before scientists flood the host egg with healthy mitochondria from the cell(s) to be cloned, or deal with them by removal much in the way they deal with the nucleus..
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What's interesting and surprising about this research is that NO mtDNA except that from the egg was found. This implies that the "foreign" mitochondria originally present were either actively killed off by something, or more likely, were not signaled to replicate at the same time all the "native" mitochondria from the egg cell were (because if they didn't replicate, they would become randomly segregated into the billions of cells making up Dolly, and would be lost). This would mean the signaling pathways telling mitochondria when to replicate are more complicated than we thought they were; i.e. we could now try to figure out what signal turns on the replication and why it only affects some mitochondria.
JMC
A lot of people are very intrigued by the idea of creating a clone of themselves and then doing a brain transplant so as to cure diseases and defeat aging.
What does this mean? This means that the clone might have different mtDNA, which generally doesn't matter. In a case where you care, you get an egg from someone with identical mtDNA (e.g., your sister).
Of course, there are a lot more issues here:
The ethics of the whole thing.
Being able to grow a brainless clone (or being willing to kill the brain of the clone).
Being able to transplant a brain without causing paralysis.
Defeating aging of the brain.
Personally, I think this is the wrong approach to this sort of thing.
Aging can probably be defeated through much less drastic measures (e.g., gene theorapy) once the process is fully understood. Think of how long plants live--there's no fundamental reason why animals must age.
Genetic disorders, excluding those caused by mutations, can be eliminated through controlled reproduction. Consider that we all have far more reproductive cells than we need. Hence, if I carry both a good and bad gene for something, why not eliminate all of my reproductive cells that carry the bad gene?
Of course, all this genetic engineering stuff already has a bad feeling associated with it, based on the last major attempt to eliminate "bad" genes. (I'm referring to WWII, of course.)