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 Shark Tagged by NSU’s Guy Harvey Research Institute Is Apparently Enjoying Time in Warm, Tropical Waters
30.03.2015 | Nova Southeastern University

nachricht Misuse of Sustainability Concept May Lead to Even More Toxic Chemical Materials
30.03.2015 | Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Experiment Provides the Best Look Yet at 'Warm Dense Matter' at Cores of Giant Planets

In an experiment at the Department of Energy's SLAC National Accelerator Laboratory, scientists precisely measured the temperature and structure of aluminum as...

Im Focus: Energy-autonomous and wireless monitoring protects marine gearboxes

The IPH presents a solution at HANNOVER MESSE 2015 to make ship traffic more reliable while decreasing the maintenance costs at the same time. In cooperation with project partners, the research institute from Hannover, Germany, has developed a sensor system which continuously monitors the condition of the marine gearbox, thus preventing breakdowns. Special feature: the monitoring system works wirelessly and energy-autonomously. The required electrical power is generated where it is needed – directly at the sensor.

As well as cars need to be certified regularly (in Germany by the TÜV – Technical Inspection Association), ships need to be inspected – if the powertrain stops...

Im Focus: 3-D satellite, GPS earthquake maps isolate impacts in real time

Method produced by UI researcher could improve reaction time to deadly, expensive quakes

When an earthquake hits, the faster first responders can get to an impacted area, the more likely infrastructure--and lives--can be saved.

Im Focus: Atlantic Ocean overturning found to slow down already today

The Atlantic overturning is one of Earth’s most important heat transport systems, pumping warm water northwards and cold water southwards. Also known as the Gulf Stream system, it is responsible for the mild climate in northwestern Europe. 

Scientists now found evidence for a slowdown of the overturning – multiple lines of observation suggest that in recent decades, the current system has been...

Im Focus: Robot inspects concrete garage floors and bridge roadways for damage

Because they are regularly subjected to heavy vehicle traffic, emissions, moisture and salt, above- and underground parking garages, as well as bridges, frequently experience large areas of corrosion. Most inspection systems to date have only been capable of inspecting smaller surface areas.

From April 13 to April 17 at the Hannover Messe (hall 2, exhibit booth C16), engineers from the Fraunhofer Institute for Nondestructive Testing IZFP will be...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

World Conference On Regenerative Medicine 2015: Registration And Abstract Submission Now Open

25.03.2015 | Event News

University presidents from all over the world meet in Hamburg

19.03.2015 | Event News

10. CeBiTec Symposium zum Big Data-Problem

17.03.2015 | Event News

 
Latest News

BLS Cargo orders 15 multisystem locomotives

30.03.2015 | Press release

Shark Tagged by NSU’s Guy Harvey Research Institute Is Apparently Enjoying Time in Warm, Tropical Waters

30.03.2015 | Life Sciences

Antarctic Ice Shelves Rapidly Thinning

30.03.2015 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>