Do plants grown from cuttings share identical DNA?
I have a rhubarb plant that's descended from my great grandfather’s garden. He originally had the plant, split it and gave some to my grandfather who in turn did the same to my father, and my father repeated this, resulting in the plant that I now have in the garden. So my question is: does my 4th generation plant share the identical DNA profile of my great grandfather’s rhubarb or will the plants evolve to create their own unique DNA?
Chris - Wow! So you have this rhubarb that you can trace all that way back. Isn't it amazing? Well, the answer is that plants obviously use DNA the same way that we do. Their cells contain a copy of their genome and that genome gets translated into the proteins that make all of the enzymes that make the biochemistry that keeps the plant alive and also, that creates its cells and so on, just like we do. But plants have a slightly lower metabolism than we do, so their DNA tends to accrue damage more slowly than ours does, so they don't tend to accrue mutations quite as quickly as we might, but that doesn't mean that they don't necessarily accrue mutations.
So when you're splitting your rhubarb, you're effectively cloning it because you're splitting an organism down the middle, and the beautiful thing about plants is that if you split them in two like that, you just get two offspring that are genetically identical because they came from one plant originally. If you then grow those up, they'll make a new plant and if you split that again, you'll get another clone of that plant, and those clones are genetically identical.
But there can be bits of those clones which can have DNA changes in them and a really good way of seeing this, [is to look at] variegated plants. Have you seen plants that have a white outer edge to a green leaf? If you look at plants like that, sometimes you'll find a stem coming off of it, where it seems to have lost the variegation. You'll see that the leaves are completely green. They've lost their white edging. Have you ever seen that?Suzy - Yes.Chris - What's actually happened there is that the genetic change which gave the plant its variegation - that white profile around the edge of the leaf - whatever that gene is, or little cluster of genes, that has changed or been mutated. It's 'reverted' as it's called back to the original stock which was the original genetic profile that gave the leaf a complete outline. There was no white edging to it. And so, the plant has a bud that gave rise to that stem produced a line which is genetically distinct. And the interesting thing is that's still connected to a plant which is variegated, but if you took a cutting from that bit of a plant, you would get a new genetic stock if you like, because it's slightly different genetically. So plants do acquire mutations. They do do it from time to time, but if you genetically sequence your rhubarb, it would be nearly identical with a few changes here and there, to the one that your grandfather was growing. And the evidence for this is that there are some plants which have propagated cloning like this for generations and generations, and generations, and they slowly evolve and adapt to the environment in which they find themselves, because there are pressures to them from the environment - pests and chemicals and nutrients and so on, but they don't change enormously.