What's the difference between a clone and a variety?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
Considering the decades of selection for disparate characteristics in Australia and Argentina, how far apart do clones, in this case Syrah/Shiraz (Australia) and Cot/Malbec (Argentina), have to be before they are considered different varieties than their French progenitors? I have tasted, with winemakers, the French-sourced clones and the New World clones grown side by side, and the differences are striking. Is there agreement among ampelographers as to what constitutes a variety vs. a clone?
—Stephen R., Aspen, Colo.
Dear Stephen,
First, I want to point out that Syrah/Shiraz and Cot/Malbec are neither different clones nor varieties, they’re just two different names for the same exact grape. It happens sometimes—other wine synonyms include Pinot Grigio/Pinot Gris and Sauvignon Blanc/Fumé Blanc.
Now, back to your question about the difference between a clone and a variety. I wanted to make sure my science was solid, so I checked in with grape DNA detective and vintner Carole Meredith. She explained that it’s not confusing at all—all clones of a variety will share the same DNA.
Explains Meredith, “A variety starts out as a vine that grows from a single seed. All vines that are propagated from that original vine by cuttings or buds will be that same variety. Over centuries of time and many thousands of vines, small spontaneous genetic changes will arise in individual vines and be perpetuated in any subsequent vines propagated from those individual vines. In that way, clonal variants will emerge, some visible or discernible by tasting and some not. No matter how many changes occur to separate these clones, they will always be clones of the original variety. They will never diverge into separate varieties. And this is clearly detectable by DNA analysis. Even dramatically different clones of Pinot Noir, for example, have the same DNA profile. And Pinot Gris, Pinot Blanc, and Meunier also have the same DNA profile as Pinot Noir. They are all clones of the same variety: Pinot.”
That said, she agrees (as do I) that clonal differences can be quite striking. Two different clones grown on the same patch of soil and made into wine using the same methods can taste very different. Send in the clones!
—Dr. Vinny