Exciting new discovery in fruit flies
August 31st 2007 07:02
From The Guardian, article by Alok Jha, science correspondent:
“Scientists have found the genes of an organism fused wholesale into the genome of an entirely separate species, raising new questions over how evolution works. The discovery suggests that simple bacteria and animals might swap entire genes more often than previously thought. Such large-scale transfer of genes would allow species to acquire entirely new functions and abilities in a very short space of time, rather than the much slower sequence of random mutations that normally evolves species over several generations.”
Continue reading here.
This is really cool stuff. It has been known for a while now that organisms can enter into intimate symbiotic relationships with one another. Our own mitochondria – the energy factories in our cells – are widely thought to have evolved from parasitic bacteria that invaded other cells, eventually entering into an arrangement with them and integrating themselves to such an extent that we would die in a matter of seconds in their absence (mitochondria sometimes get up to mischief, though. Since they are almost always inherited maternally, they are under selection for the ability to distort the sex ratio in favour of females. Nuclear genes fight back, though, as they are under selection to restore the balance).
Gene transfer mechanisms in bacteria are more or less well understood. They range from transformation, in which bacteria absorb naked DNA through their outer surface and then have this DNA integrated into their chromosomes through a process known as recombination; transduction, in which viruses that attack bacteria – these viruses are known as phages – implant some DNA gotten from a previous a infection into the new host; and conjugation, in which two bacteria link together and transfer plasmids, which are circular pieces of DNA containing genes that confer such abilities as antibacterial resistance (this class are called R-factors, and they are a major concern for disease control efforts) and special metabolic functions.
In “higher” organisms, gene transfer of this sort has been known to occur via viral infections (our own genomes are host to entities known as endogenous retroviruses, which are mainly defunct copies of retroviruses – the sorts that integrate into our chromosomes to be reactivated later during the “virulent” phase, in which they use the host's cellular machinery to make copies of themselves that then go on to infect other cells. There have been cases of the same genes found in distantly related species but not in closer relatives of either group, and viruses have been suspected (the other possibility is convergent evolution, where the genes are independently evolved in the two lineages, but geneticists have sophisticated models that give them some indication of what explanation is more likely in any given case). Could this be much more common than previously thought?
But this latest news takes it to a whole new level, because here we see not just genes making themselves at home, but an entire genome, encoding for a whole “separate” organism living within another. This is perhaps something we should readily expect to happen when a parasite must pass through the same reproductive bottleneck as the nuclear DNA. Their fates are now intimately tied, and selection will favour any tendency for integration of the two since what is good for one will tend to be good for the other. Maybe if we were to come back in thousands of years, we will find that Wolbachia is no longer a proper bacterium in its own right, but something more like mitochondria. Interestingly, it is thought that over evolutionary time, most mitochondrial genes migrated (perhaps via transposons, or “jumping genes”) over to the nucleus. Could this latest indicate a sort of fast-forward repeat of that process?
“Scientists have found the genes of an organism fused wholesale into the genome of an entirely separate species, raising new questions over how evolution works. The discovery suggests that simple bacteria and animals might swap entire genes more often than previously thought. Such large-scale transfer of genes would allow species to acquire entirely new functions and abilities in a very short space of time, rather than the much slower sequence of random mutations that normally evolves species over several generations.”
Continue reading here.
This is really cool stuff. It has been known for a while now that organisms can enter into intimate symbiotic relationships with one another. Our own mitochondria – the energy factories in our cells – are widely thought to have evolved from parasitic bacteria that invaded other cells, eventually entering into an arrangement with them and integrating themselves to such an extent that we would die in a matter of seconds in their absence (mitochondria sometimes get up to mischief, though. Since they are almost always inherited maternally, they are under selection for the ability to distort the sex ratio in favour of females. Nuclear genes fight back, though, as they are under selection to restore the balance).
Gene transfer mechanisms in bacteria are more or less well understood. They range from transformation, in which bacteria absorb naked DNA through their outer surface and then have this DNA integrated into their chromosomes through a process known as recombination; transduction, in which viruses that attack bacteria – these viruses are known as phages – implant some DNA gotten from a previous a infection into the new host; and conjugation, in which two bacteria link together and transfer plasmids, which are circular pieces of DNA containing genes that confer such abilities as antibacterial resistance (this class are called R-factors, and they are a major concern for disease control efforts) and special metabolic functions.
But this latest news takes it to a whole new level, because here we see not just genes making themselves at home, but an entire genome, encoding for a whole “separate” organism living within another. This is perhaps something we should readily expect to happen when a parasite must pass through the same reproductive bottleneck as the nuclear DNA. Their fates are now intimately tied, and selection will favour any tendency for integration of the two since what is good for one will tend to be good for the other. Maybe if we were to come back in thousands of years, we will find that Wolbachia is no longer a proper bacterium in its own right, but something more like mitochondria. Interestingly, it is thought that over evolutionary time, most mitochondrial genes migrated (perhaps via transposons, or “jumping genes”) over to the nucleus. Could this latest indicate a sort of fast-forward repeat of that process?
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