Thursday, 7 March 2013

Coffee's chromosomal complexity: is Coffea smarter than a swamp wallaby?


For a couple of weeks, there is a thing called the Urban Coffee Farm and Brew Bar in Queensbridge Square, just south of the Yarra River in Melbourne. It contains plenty of coffee plants, plenty of roasted coffee and lots of coffee-rich information.

Most of the coffee information is on the mark. However I think this line overplays things a little: The Arabica bean has 44 chromosomes...its genetic complexity contributing to the varietal's depth of flavour.

The implication being, I presume, that because coffee has only two less chromosomes that a human it must be a rather complex bean indeed.

Wikipedia and other information sites list a fern, Ophioglossum (the Adder's Tongue), as having the largest number of chromosomes of any living organism. Its diploid number (i.e. the double set of chromosomes that organisms with chromosomes tend to have in their dominant phase) is 1,440. Yep, one thousand, four hundred and forty!


Ophioglossum is not much to look at. It's in the middle of this picture I took at the Grampians a few years back. Each of the two plants has a single frond with a spore-bearing stalk (you can just see the spore packages yellowing up in the righ-hand plant). So you might wonder why it carries so many of these short ropes of coiled DNA.

It turns out there are multiple sets of the basic paired group of chromosomes, something we call polyploidy. The massive number we count today would have been accumulated overtime through duplication from a base diploid number of 30, or something even less than this at first, from a mix of 4, 5 and 6. Why it needs to have have so many copies I don't know.

Us humans have one set of 46. This is a couple less than gorillas, chimpanzees and potatoes at 48. A carp has 104, a shrimp around 90, a dog 78 and a fruit fly 8. The female Jack Jumper Ant has a single pair of chromosomes.

You get the idea. The number of chromosomes doesn't tell us much about the complexity, intelligence or size of the organism. As to depth of flavour, I suspect not either.

I gather a coffee plant (Coffea) with 44 chromosomes has double what we might call the standard set. It's ancestors presumably had 22. Neither number tells you much about its biology or genetic potential.

That said, it's a fun game to play and a basic set of 22 chromosomes is nothing to sniffed at. After all, that's how many you'll find in a green bean or an opossum, and double that of a Swamp Wallaby.

So is a coffee bean smarter than a swamp wallaby? And do humans becomes six times smarter than marsupials after an espresso or two? Not sure, but isn't coffee great!

4 comments:

Dave Bright said...

Brilliant, Tim!
I commend you on the breadth and depth of the information you post on your blog.
I wonder what humans would look like if we had 1,440 chromosomes! The mind boggles!!
I look forward to reading many more interesting comments on Talking Plants.

Tim Entwisle said...

Thanks Dave!

Gareth said...

'Ophioglossum is not much to look at..' agreed when looking at your photo but do you remember the one oft displayed in the Pyramid in a hanging basket? This is a gorgeous fern, an australian/asiatic species, O.pendulum. Often grows out the bottom of Platycerium and birds nest fern clumps.

Tim Entwisle said...

Thanks Gareth (sorry, not checking comments for a while...). I'd forgotten that one. Even my little one is cute in the right setting...
Tim