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Researchers confirm key component of evolutionary theory

A technique known as gene conversion makes up for an asexual organism's lack of sex.
By Brooks Hays   |   Jan. 26, 2016 at 4:29 PM

GLASGOW, Scotland, Jan. 26 (UPI) -- The "Meselson effect" is a key aspect of evolutionary theory. It predicts that pairs of chromosomes in asexual organisms diverge and evolve independently, becoming increasingly dissimilar over time.

The effect is named after accomplished geneticist Matthew Stanley Meselson, who first conceived of the phenomenon some 20 years ago, but until now, scientists haven't been able to offer concrete evidence of the effect.

Researchers at the University of Glasgow successfully demonstrated the effect in a parasite known as Trypanosoma brucei gambiense, or T.b. gambiense. It's the first time the effect has been proven in a living organism. The parasite causes sleeping sickness in humans.

Scientists analyzed the genomes of 85 different parasite samples collected from Guinea, Cote d'Ivoire and Cameroon between 1952 and 2004.

The analysis -- detailed in the journal eLife -- revealed divergent chromosomes, devoid of genetic recombination. The research suggests the parasite is a subspecies evolved from a single individual no longer than 10,000 years ago.

"It was around this time that livestock farming was developing in West Africa, allowing the parasite, which was originally an animal organism, to 'jump' from one species to the other via the Tsetse fly," lead study author Willie Weir said in a press release.

"Since then, mutations have built up and the lack of sexual recombination in T.b. gambiense means that the two chromosomes in each pair have evolved independently of each other, demonstrating the Meselson effect," Weir added.

Researchers say the parasite's inability to recombine genes hinders its ability to adapt and develop resistance to multiple drugs.

Sex is the predominant form of reproduction for a reason. It helps organisms persist, enables lineages to continue.

"An organism's genetic blueprint is encoded in DNA packaged within structures called chromosomes. Most organisms have two copies of each chromosome and, through sexual reproduction, the DNA within the chromosomes can recombine randomly, in effect shuffling the deck of DNA cards," Weir explained. "This process generates genetic diversity and, through natural selection, undesirable combinations and mutations are eliminated from the population, promoting long-term survival of the species."

The Meselson effect predicts that abstinence can only work for so long, and that asexual organisms should eventually become extinct. Eventually, the parasite that causes sleeping sickness should be no more. But researchers aren't yet able to predict when the end will come.

The latest research suggests the parasite uses a technique known as gene conversion to maintain genetic health. The parasite is able to identify gene mutations and replace them by copying and pasting healthy sequences from the chromosome's partner.

Researchers say more research is necessary to determine the long-term consequences of an organism's reliance on genetic conversion.

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