Featured Research

from universities, journals, and other organizations

Evolution Of Sex Chromosomes: The Case Of The White Campion

Date:
February 2, 2005
Source:
Public Library Of Science
Summary:
Similarities in sex chromosome evolution have been reported between birds and mammals (although in birds, females are the heterozygous sex). In a new study, Michael Nicolas and colleagues uncover striking parallels in the details of sex chromosome evolution between mammals and a far more distant group: plants.

Flowers of Silene species, clockwise from top left: male flowers of S. latifolia and S. dioica, hermaphrodite flower of S. vulgaris, male flower of S. diclinis.
Credit: Photo s courtesy of Public Library Of Science

There are many different sex-determining systems in plants and animals with separate sexes (dioecious species). In some species, environmental factors activate sex-determining genes that trigger expression of genes leading to male or female development. Other species have evolved specialized sex chromosomes. In the well-known X-Y system of mammals, individuals inheriting a Y chromosome become males, and XX individuals become females.

Related Articles


Sex chromosomes have arisen independently in many taxonomic groups. It is an interesting question whether the same mechanisms were involved each time. Similarities in sex chromosome evolution have been reported between birds and mammals (although in birds, females are the heterozygous sex). In a new study, Michael Nicolas and colleagues uncover striking parallels in the details of sex chromosome evolution between mammals and a far more distant group: plants.

Sex chromosomes are an oddity in flowering plants. They are limited to dioecious species, a subset of plants that carry male and female organs (stamens and carpels, respectively) on separate individuals (most flowering plants are hermaphrodites). The genus Silene, which includes the White Campion, includes both dioecious and hermaphrodite species. The authors focus on three dioecious species, Silene dioica, S. latifolia, and S. diclinis, which share an X-Y sex-determination system where Y specifies maleness.

The theory of sex chromosome evolution holds that sex chromosomes were once homologs (a pair of equivalent autosomes—the non-sex chromosomes) that evolved different morphology and gene content because they lost their ability to recombine. Suppression of recombination is thought to start around the sex-determining region, but may eventually affect much of the sex chromosomes. Recombination is a key genetic process in which two chromosomes pair and exchange their sequences. In the absence of recombination, the two chromosomes of a pair evolve separately.

In the case of mammals, whose sex chromosomes evolved about 320 million years ago, loss of recombination led to widely diverged X and Y chromosomes that pair only over a very small region, the pseudoautosomal region (PAR; because in this region the X and Y still behave like autosomes). The X and Y chromosomes of dioecious Silene species are morphologically distinct, like those of mammals, and they also have a PAR and a nonrecombining region. Nicolas and colleagues' results shed some light on how recombination suppression evolved on the Silene sex chromosomes.

The authors studied four genes outside the PAR on the Silene X chromosomes that are also present on their Y chromosomes. They mapped the genes relative to the PAR and compared the nucleotide sequences of the X and Y version of each gene in each species. As expected of sequences that no longer recombine, the X and Y versions of each gene have diverged. Strikingly, the extent of nucleotide divergence increases with the gene's distance from the PAR.

Evolutionary biologists use sequence divergence as a clock: the longer two originally identical sequences have been isolated from one another, the more independent mutations they accumulate. The picture that emerges from the Silene data is one of a progressive suppression of recombination, gradually diminishing the PAR. A similar scenario has been proposed in mammals and birds. However, the authors estimate that the Silene sex chromosomes started diverging only 10 million years ago. The Silene chromosomes might therefore offer a better chance to observe recombination suppression in its early stages, and perhaps to get at its mechanisms.

The authors also report evidence for some degeneration of the Silene Y chromosome genes. Y degeneration is well documented in mammals, in which most X-linked genes have no Y-linked counterparts. Understanding X-Y divergence in Silene species may thus shed light on the evolution of sex chromosomes in vertebrates as well.


Story Source:

The above story is based on materials provided by Public Library Of Science. Note: Materials may be edited for content and length.


Cite This Page:

Public Library Of Science. "Evolution Of Sex Chromosomes: The Case Of The White Campion." ScienceDaily. ScienceDaily, 2 February 2005. <www.sciencedaily.com/releases/2005/02/050201112231.htm>.
Public Library Of Science. (2005, February 2). Evolution Of Sex Chromosomes: The Case Of The White Campion. ScienceDaily. Retrieved October 31, 2014 from www.sciencedaily.com/releases/2005/02/050201112231.htm
Public Library Of Science. "Evolution Of Sex Chromosomes: The Case Of The White Campion." ScienceDaily. www.sciencedaily.com/releases/2005/02/050201112231.htm (accessed October 31, 2014).

Share This



More Plants & Animals News

Friday, October 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

How A Chorus Led Scientists To A New Frog Species

How A Chorus Led Scientists To A New Frog Species

Newsy (Oct. 30, 2014) A frog noticed by a conservationist on New York's Staten Island has been confirmed as a new species after extensive study and genetic testing. Video provided by Newsy
Powered by NewsLook.com
Surfer Accidentally Stands on Shark, Gets Bitten

Surfer Accidentally Stands on Shark, Gets Bitten

AP (Oct. 30, 2014) A 20-year-old competition surfer said on Thursday he accidentally stepped on a shark's head before it bit him off the Australian east coast. (Oct. 30) Video provided by AP
Powered by NewsLook.com
Ebola Inflicts Heavy Toll on Guinean Potato Trade

Ebola Inflicts Heavy Toll on Guinean Potato Trade

AFP (Oct. 30, 2014) The Ebola epidemic has seen Senegal and Guinea Bissau close its borders with Guinea and the economic consequences have started to be felt, especially in Fouta Djallon, where the renowned potato industry has been hit hard. Duration: 02:01 Video provided by AFP
Powered by NewsLook.com
Genetically Altered Glowing Flower on Display in Tokyo

Genetically Altered Glowing Flower on Display in Tokyo

Reuters - Innovations Video Online (Oct. 30, 2014) Just in time for Halloween, a glowing flower goes on display in Tokyo. Instead of sorcery and magic, its creators used science to genetically modify the flower, adding a naturally fluorescent plankton protein to its genetic mix. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins