Studies reveal that there is an evolutionary arms race going on between genes and ‘selfish genetic elements. Many genes are selfish and only focused on their spread and survival. Read and find out who’s winning the race.
What is the evolutionary arms race?
While the ‘parasites of the genome’ are not new news, a new study highlights more details on their inner working. Researchers looked into the genomes of three closely related fruit fly (Drosophila) species. Why fruit flies and not human genomes? Well, Drospohila’s genome and our genome is a 60 percent match. Moreover, 75 percent of their genes match with human genes that cause diseases making them the perfect model organism for research. Additionally, unlike humans, they have very short reproductive cycles (less than two weeks). Hence, it is very easy to study generations of fruit flies in a short time.
The new study revealed that each fly species had 5 to 12 meiotic drive genes on their X chromosomes. The newly discovered meiotic drive genes are selfish and sneaky. They spread and make their presence in more than the standard 50 percent in the offspring, asserting their dominance. “We have found that an evolutionary arms race has led to a proliferation of meiotic drive genes on the X chromosome and suppressor genes elsewhere in the genome,” said Christina Muirhead. Muirhead is a theoretical population geneticist and an evolutionary biologist at the University of Rochester. The study is published in the Nature ecology and evolution journal.
What are the selfish genes up to?
These selfish genes are related to the meiotic drive gene known as the ‘disorder on X’ or Dox gene. They are found on the X chromosome and kill sperms that bear the Y chromosome. Hence, due to the similarity of attack, the selfish genes are known as Dox-like or Dxl. Studies show that the Dxl genes produce histone and this is interfering with immature Y-bearing sex cells. Due to this interfering, the sex cells die and future generations may have fewer sons than daughters.
“The drive genes get an evolutionary advantage by killing Y-bearing sperm. But the individuals carrying the drive genes suffer reduced fertility, and the population becomes increasingly female-biased, risking eventual extinction,” said Daven Presgraves. Presgraves is an evolutionary geneticist from the University of Rochester. They also found that the Dxl gene duplicates were counterattacking original Dxls by pretending to be selfish Dxl genes. However, duplicate genes were silencing the real ones with RNA interference hence stopping a modification.
This means that the fruit fly genome was evolving and managed to suppress the selfish parts to ensure that they survive. “Similar repetitive gene copies like the Dxl genes that selfishly bias sex ratios are common to the X and Y chromosomes of great apes and humans. These are just one line of evidence that evolutionary arms races have important consequences for genome evolution,” explained Presgraves. However, further research is needed to verify if something similar is happening in the human genome.