More evidence of an evolutionary `arms race' between genes and selfish
genetic elements
Biologists further prove that genes develop weapons to combat the
`parasites' that litter the human genome.

Date:
November 12, 2021
Source:
University of Rochester
Summary:
Researchers discover further evidence of an evolutionary arms race
within organisms -- and the mechanisms at play in this arms race --
to combat selfish genetic elements.



FULL STORY ==========================================================================
The human genome is littered with selfish genetic elements, which do
not seem to benefit their hosts, but instead seek only to propagate
themselves.


========================================================================== These "parasites of the genome" can wreak havoc at the cellular level by distorting sex ratios or causing harmful mutations, and can even lead to
a species' extinction. But, as researchers at the University of Rochester report, species evolve mechanisms to fight back.

In a new paper published in Nature Ecology and Evolution, Daven
Presgraves, a University Dean's Professor in the Department of Biology
at the University of Rochester, and Christina Muirhead, a computational biologist and population geneticist in Presgraves's lab and the first
author on the paper, present further evidence of an evolutionary arms
race within organisms -- and the mechanisms at play in this arms race --
to combat selfish genetic elements.

"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," Muirhead says.

Drosophilais fruitful and multiplies -- which is ideal for studying
genetics The researchers studied the genomes of three closely related
species of Drosophila (fruit flies). Fruit flies share about 70 percent
of the same genes that cause human diseases and are similar to humans
on the molecular level.

Because fruit flies have such short reproductive cycles -- less than
two weeks -- scientists can create generations of the flies in a short
time. These key characteristics make the insects ideal models for learning
more about human genetics.



==========================================================================
The researchers discovered that each of the species of fruit flies they
studied has 5 to 12 meiotic drive genes on the X chromosomes. The meiotic
drive genes - - a type of selfish genetic element -- cheat by getting into
more than the typical 50 percent of offspring in the next generation. This allows the genes themselves to spread rapidly through a population.

The meiotic drive genes that the researchers studied are related to
a meiotic drive gene called Dox -- "distorter on the X" -- which is
found on the X chromosome and kills Y chromosome-bearing sperm. The
researchers called their newly discovered genes 'Dox-like,' or 'Dxl'
for short. The Dxl genes produce a protein called a histone that disrupts normal DNA packaging in Y-bearing spermatids -- immature male sex cells -- leading to sperm death. Killing Y- bearing sperm means that subsequent generations will have mostly daughters and few sons.

The Dxl genes work only to propagate themselves, however, and don't
"realize" that this may lead them on a path that could eventually take
their host species -- and themselves -- to extinction.

"The drive genes get an evolutionary advantage by killing Y-bearing
sperm," Presgraves says. "But the individuals carrying the drive genes
suffer reduced fertility, and the population becomes increasingly female-biased, risking eventual extinction." Duplicate Dxl genes play
defense Dxl genes skew sex ratios to increase the rate at which they get
passed on, but the researchers uncovered another surprising dynamic. The species of Drosophila they studied have evolved a defense against the
selfish genetic elements. This defense comes in the form of genes that are duplicates of the Dxl genes, but with an important modification. Much like
the mythical Trojan Horse, the duplicate genes masquerade as Dxl genes,
but contain a stealthy weapon. Instead of expressing Dxl proteins, the
genes express small RNAs that silence the Dxl genes via RNA interference.

The research is further evidence that microscopic evolutionary arms
races are taking place within organisms: selfish genetic elements evolve
to benefit themselves, and the rest of the genome evolves suppressors
to quell them. The selfish genetic elements then evolve to overcome
the suppressor, the suppressor has to evolve to keep pace, and so
on."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," Presgraves says. "These are just one line of evidence that evolutionary arms races have important consequences for genome evolution." ========================================================================== Story Source: Materials provided by University_of_Rochester. Original
written by Lindsey Valich. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Christina A. Muirhead, Daven C. Presgraves. Satellite DNA-mediated
diversification of a sex-ratio meiotic drive gene family in
Drosophila.

Nature Ecology & Evolution, 2021; DOI: 10.1038/s41559-021-01543-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211112100542.htm

--- up 1 day, 2 hours, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)