Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Evolutionary biologists glimpse early stages of Y-chromosome degeneration

14.05.2014

Findings shed light on the evolutionary history of sex chromosomes

In many species, the possession of X and Y chromosomes determines whether an individual develops into a male or female. In humans, for example, individuals who inherit their father's Y chromosome become male (XY), and individuals who inherit their father's X chromosome become female (XX).

This system of sex determination has evolved independently multiple times and a striking feature of its evolution is that Y chromosomes have degenerated genetically, losing many genes over time. What is not well understood, however, is what happens to the Y chromosome during the earliest stages of this evolution, or the time scales over which degeneration occurs.

Now, University of Toronto (U of T) researchers have found a way to shed light on the early stages of degeneration, by investigating the process in plants.

"In humans, the Y chromosome has undergone extensive gene loss over its roughly200-million-year evolutionary history, and now retains only about three per cent of its ancestral genes. We know very little about the early stages of the process, however, because it happened so long ago," said U of T Department of Ecology & Evolutionary Biology (EEB) professor Spencer Barrett, co-investigator of a study published today in Proceedings of the National Academy of Sciences. "The most well-studied Y chromosomes, including those in humans and other animal species, began degenerating hundreds of millions of years ago. Not so with plants."

"The emergence of separate sexes in plants is a relatively recent evolutionary innovation, making them ideal for this study," said Barret. "Only about six per cent of flowering plants have males and females. The remainder are hermaphrodites."

The scientists used a plant species with separate sexes whose X and Y chromosomes probably first evolved around 15 million years ago at the most, making them relatively young compared to those in animals.

"We tested for Y-chromosome degeneration in Rumex hastatulus, an annual plant from the southern USA commonly known as heartwing sorrel. We found that genes on the Y chromosomes have already started to undergo genetic degeneration, despite their relatively recent origin," said Josh Hough, a PhD candidate in U of T's Department of Ecology & Evolutionary Biology and lead author of the study. "Importantly, our results indicate that the extent of this degeneration depends on how long ago the genes on the sex chromosomes stopped recombining with each other."

The theory of sex chromosome evolution holds that Y-chromosome degeneration occurs as a result of X and Y chromosomes failing to recombine their genes during reproduction. Recombination is a key genetic process in which chromosomes pair and exchange their DNA sequences, and it occurs between all other chromosomes in the genome, including the X chromosome, which recombines in females. This genetic mixing has become suppressed between the X and Y chromosomes, however, probably because they contain genes that affect 'femaleness' and 'maleness', and combining these genes onto a single chromosome can cause infertility problems.

"Suppressing recombination between the X and Y makes sense because it prevents genes that determine female-specific traits from occurring on the Y chromosome," said Hough. But without recombination natural selection becomes less efficient, and harmful mutations cannot be removed from the Y chromosome. As a result, genes on the Y chromosome eventually become impaired in function or lost entirely."

The researchers crossed multiple male and female plants and then traced the inheritance of genes by sequencing the DNA in parents and their offspring. This allowed them to find which genes were located on the sex chromosomes because they segregate differently than genes on other chromosomes. Computer-assisted analyses of the genetic sequences enabled the scientists to then test for gene loss, loss of gene function, the accumulation of mutations, and other harmful changes on the sex chromosomes.

Suppressed recombination between X and Y chromosomes occurred much more recently in plants than in animals, so the scientists were able to get a unique glimpse of what happens during the very earliest stages of Y-chromosome degeneration.

"In addition to being much younger than in animals, the sex chromosomes in Rumex hastatulus are particularly interesting because of the recent emergence of a new sex chromosome system, in which some males carry a second, even younger, Y chromosome," says Hough. "This allowed us to compare the two Y chromosomes and assess the time scales over which genes are deteriorating."

"The genes on the second Y chromosome are very new arrivals, having arisen within a single species", says EEB professor Stephen Wright, another investigator on the study. "This gave us a key time point to understand the chronology of Y-chromosome evolution. Remarkably, even these genes were already showing early signs of degeneration."

###

Additional researchers contributing to this collaborative effort included postdoctoral fellow Jesse Hollister and computational biologist Wei Wang, both of EEB. The findings are reported in the article "Genetic degeneration of old and young Y chromosomes in the flowering plant Rumex hastatulus" published online May 13 in Proceedings of the National Academy of Sciences. The research was supported by Discovery grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) to Barrett and Wright.

MEDIA CONTACTS:

Josh Hough
Department of Ecology and Evolutionary Biology
University of Toronto
416-978-7177 (office)
josh.hough@utoronto.ca

Spencer C. H. Barrett
Department of Ecology and Evolutionary Biology
University of Toronto
416-978-4151 (office)
spencer.barrett@utoronto.ca

Stephen I. Wright
Department of Ecology and Evolutionary Biology
University of Toronto
(416) 946-8508 (office)
stephen.wright@utoronto.ca

Sean Bettam
Communications, Faculty of Arts & Science
University of Toronto
416-946-7950
s.bettam@utoronto.ca

Sean Bettam | Eurek Alert!
Further information:
http://www.utoronto.ca

Further reports about: Biology DNA EEB Ecology Evolutionary Toronto Y-chromosome animals chromosomes female genes recombination species

More articles from Life Sciences:

nachricht More genes are active in high-performance maize
19.01.2018 | Rheinische Friedrich-Wilhelms-Universität Bonn

nachricht How plants see light
19.01.2018 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>