Navigation Links
Evolutionary biologists glimpse early stages of Y-chromosome degeneration

TORONTO, ON 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."


Contact: Sean Bettam
University of Toronto

Related medicine news :

1. A Revolutionary Dietary Paradigm: New Cookbook Features A SOS-free (Salt, Oil, Sugar ) Diet That Delivers the Optimal Food Plan for Renewing Health
2. Vygone Presents a Revolutionary Electro Waveform Device to Help Treat Molluscum Contagiosum Lesions
3. Evolutionary information improves discovery of mutations associated with diseases
4. Human Intellect Backsliding From Lack of Evolutionary Pressure: Study
5. Naturel Collagen Canada Unveils C RUM, the Newest Addition to the Revolutionary Natural Collagen Skin Care Product Line
6. U of T Researchers uncover major source of evolutionary differences among species
7. Brand id¦Strategic Partners Launches Revolutionary Personal Branding Success Program for Women
8. Mount Sinai Grad Student, 25, Named to Forbes ’30 Under 30’ In Science and Healthcare for ‘Revolutionary New Ideas’
9. Revolutionary techniques could help harness patients own immune cells to fight disease
10. Dr. Harvey’s Launches "Oracle": a Revolutionary Freeze-Dried, Highly Nutritious and Protein-Rich Line of Complete Foods for Dogs and Cats
11. How can evolutionary biology explain why we get cancer?
Post Your Comments:
(Date:6/24/2016)... San Francisco, CA (PRWEB) , ... June 24, ... ... at CitiDent, is now offering micro-osteoperforation for accelerated orthodontic treatment. Dr. Cheng has ... , self-ligating Damon brackets , AcceleDent, and accelerated osteogenic orthodontics. , ...
(Date:6/24/2016)... ... ... makers of Topricin and MyPainAway Pain Relief Products, join The ‘Business for a Fair Minimum ... by 2020 and then adjusting it yearly to increase at the same rate as the ... wage floor does not erode again, and make future increases more predictable. , The company ...
(Date:6/24/2016)... Georgia (PRWEB) , ... June 24, 2016 , ... ... awards today at the Clinical Decision Making in Emergency Medicine conference in Ponte ... have authored journal articles published in Emergency Medicine Practice and Pediatric ...
(Date:6/24/2016)... ... June 24, 2016 , ... Puradigm® ... Group (TGIG), has initiated cultivation and processing operations at its production facility, and ... Nevada. , Puradigm is the manufacturer of a complete system of proactive air ...
(Date:6/24/2016)... ... ... recruitment firm Slone Partners is pleased to announce the placement of Suzanne ... of North American Capital Sales at HTG Molecular . , In ... commercialization of the HTG EdgeSeq system and associated reagents in North America. , Headquartered ...
Breaking Medicine News(10 mins):
(Date:6/23/2016)... Roche (SIX: RO, ROG; OTCQX: RHHBY) announced ... BRAHMS PCT (procalcitonin) assay as a dedicated testing solution ... this clearance, Roche is the first IVD company in ... sepsis risk assessment and management. PCT is ... levels in blood can aid clinicians in assessing the ...
(Date:6/23/2016)... 2016 Bracket , a leading clinical trial ... clinical outcomes platform, Bracket eCOA (SM) 6.0, at the ... – 30, 2016 in Philadelphia , Pennsylvania.  ... Assessment product of its kind to fully integrate with RTSM, ... eCOA 6.0 is a flexible platform for electronic clinical outcomes ...
(Date:6/23/2016)... , June 23, 2016 Revolutionary ... Oticon , industry leaders in advanced audiology ... of Oticon Opn ™, the world,s first internet ... possibilities for IoT devices.      (Photo: ... introduces a number of ,world firsts,: , ...
Breaking Medicine Technology: