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.

Comments

Not unexpected

[Anonymous Coward]

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.

Yes it is

[chandoni]

All the nuclear DNA came from one sheep, but because of the way the clone was made, the mitochondria came from both the egg (most of them) and the cell that was fused with it (a smaller number). Mitochondria replicate some time in the cell cycle (along with all the other organelles), so one would probably expect all cells in Dolly to have the same ratio of mtDNA types as the original fused cell.

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