When people hear the word “mutant,” there’s not a lot of positive association that goes on.
Some might think more along the lines of horrific animal crossbreeds, disgusting monsters, and even Michael Phelps (half fish, half human—all really weird).
But say that in front of Dr. Chris Hittinger or Dr. Mark Johnston, and they’ll start going on about yeast and ‘BUGNPs’ till their voices are hoarse.
This mutant craze is thanks to a discovery the pair stumbled upon while studying a certain species of yeast. “We had this version of yeast that grows on galactose,” Johnston said.
Galactose is a form of carbohydrate that isn’t used by this species of yeast. So the fact that it grew on this was equivalent to raising a baby by feeding it sawdust. It just doesn’t work.
When they found this, they didn’t believe their own work. “We said, ‘this can’t be right,’” Johnston said.
When they sequenced the genome to verify the results, however, it only became stranger and stranger.
“[This] yeast species we sequenced had genes required for using galactose,” Johnston said. This was an anomaly, as all other known species of yeast have pseudogenes where those galactose processing genes are.
“If a gene is no longer needed, it’ll pick up lots of mutations over time,” Johnston said. “This is what’s called a pseudogene. You can still recognize it, but it has enough mutations so that they don’t make functional proteins.”
In this species, however, that wasn’t the case. The genetic material needed was still there.
And this wasn’t just one gene. It was five. Five genes, spread across several chromosomes.
“Basically, what we’ve found is sort of a novel type of genetic variation,” said Hittinger.
“Really striking thing is that most genetic variations that get maintained are on one gene. This is scattered over four chromosomes and maintained over millions of years.”
The odds of this mutation happening by chance and staying that way? Next to impossible.
So what’s going on?
The team refers to the mutations as a BUGNP—a balanced unlinked gene network polymorphism. It’s sort of a mouthful; let’s break it down.
The “B” and “P” parts are for “balanced polymorphism,” a phenomenon that some may have heard of, but not know by name. It’s the reason we have sickle cell anemia.
Natural selection in a nutshell: The better a gene is for an individual, the more likely it will benefit its offspring and be replicated, making the trait more common among the entire species.
So why would something like sickle cell anemia be passed on?
To get it, you need both of the genes. If you only get one, on the other hand, you become more resistant to malaria—a trait that would help you out if you lived in, say, Africa.
“In some situations, you have a case where an optimal version of a gene depends on several factors,” Hittinger said. “But in some cases, there is no optimal version.”
Because having the gene gives the individual an advantage, even if having two doesn’t, the gene will sometimes be kept in the evolutionary flow: a balanced polymorphism.
That other part, “unlinked gene network,” simply refers to the complexity of the polymorphism. It’s not only one gene on one chromosome. Try five on several.
This is the first time anything like this has ever been documented. Not only does it help scientists understand evolution and its mechanisms, but it could help malaria researchers look at the mechanisms that keep the sickle cell anemia gene in our global gene pool.
So where’s the benefit, yeast-wise, as far as not being able to feed off of galactose?
“If you can’t use galactose, you don’t want to put energy towards it at all,” Johnson said.
Simply put, the reason it is an advantage for some yeast not to use galactose is to save energy.
It would be the same idea as us putting energy towards being able to eat diamonds for nutritional value. Yeah, sure, it wouldn’t hurt. But how often is that going to be useful?
There’s no point in building an ark if there ain’t no flood.
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