When you've doubled your genes, what's 1 chromosome more or less?

Sep 14, 2009

An individual with Down syndrome and a male calico cat have one thing in common -- each has an extra chromosome. For animals, most instances of an extra chromosome result in birth defects or even death, but plants are another matter entirely. Many plants are able to survive the presence of an extra copy of their entire genome (known as polyploidy) and are often even more vigorous as a result. For plants, the process of polyploidy often results in a new species, making it an important mechanism in evolution. In fact, over 80% of plants may be a product of polyploidy.

However, this extra set of chromosomes can sometimes cause confusion during meiosis, the process by which sets of chromosomes are divided up to produce egg and , with half the number of chromosomes present in a mature plant. Many recent studies have examined the effects of polyploidy on meiosis. A recent study by Drs. Andreas Madlung, Kirsten Wright, and J. Chris Pires, published in the September issue of the , examines the effects of polyploidy on a more common type of cell division, mitosis--the process of cell division that results in daughter cells that are identical to the parent cell--which allows the plant to grow and develop.

"We had been working on genomic responses to allopolyploidy for many years in newly formed allopolyploids and had noticed some instabilities during meiosis and gamete formation in newly formed allopolyploids," Madlung said. "The commonly held belief is that in established allopolyploids, incompatibilities of the two parental genomes somehow are reconciled during the evolution of the allopolyploid species but there is only relatively little data in the literature that supports this notion.

"Our work shows that even established polyploids can harbor considerable genomic instabilities, but interestingly this is not always the case either, as the different responses in different sibling lines show."

Madlung and colleagues studied whether mitosis proceeds normally in newly formed polyploids and whether there are differences between mitosis in newly formed polyploids and polyploids that were established long ago. They examined a species of rock cress, Arabidopsis suecica, a polyploid with 26 chromosomes that is both found in nature and can also be resynthesized in the laboratory. Arabidopsis suecica was formed from the hybridization of a tetraploid accession of Arabidopsis thaliana, a species with 20 chromosomes, and the tetraploid Arabidopsis arenosa, a species with 32 chromosomes.

Madlung and colleagues found that a small number of cells in both natural and in one of two newly formed A. suecica had either extra chromosomes or were missing chromosomes. Interestingly, in examinations of the progenitor species of A. suecica, Madlung and colleagues found many cells with differing numbers of chromosomes in A. arenosa; however, most cells in individuals of both diploid and tetraploid A. thaliana had the expected 10 or 20 , respectively. In individuals with unexpected chromosome numbers, the numbers varied between cells like in a mosaic, suggesting that these changes are not stable.

"Maybe the most interesting result to me is the fact that plant cells can sustain a large amount of aneuploidy in their tissue without detrimental phenotypic consequences," Madlung said. "We were also surprised to notice that the tissue we looked at consisted of a mosaic of different types of aneuploid and euploid cells. The fact that the plants were quite fertile indicates that possibly the euploid cells contribute the majority of cells to what later becomes the gametes."

These results suggest that slight changes in chromosome number in an individual's non-sex cells are tolerated but are not fixed, providing new insights into how polyploidy and genomic change can lead to evolutionary change and possibly ultimately affect plants' fitness and vigor.

More information: www.amjbot.org/cgi/content/full/96/9/1656

Source: American Journal of Botany

Explore further: Free the seed: OSSI nurtures growing plants without patent barriers

add to favorites email to friend print save as pdf

Related Stories

Double identities lie behind chromosome disorders

Jul 08, 2007

Chromosome disorders in sex cells cause infertility, miscarriage and irregular numbers of chromosomes (aneuploidy) in neonates. A new study from Karolinska Institutet published in the scientific journal Nature Genetics shows ...

Is this the beginning of the end of plant breeding?

Jun 09, 2009

No human is a clone of their parents but the same cannot be said for other living things. While your DNA is a combination of half your mother and half your father, other species do things differently. The advantage of clonal ...

Protein role in meiosis re-evaluated by researchers

Apr 17, 2008

Proteins that control cell division play a far more nuanced role than researchers previously thought in the process that gives rise to reproductive cells, according to new findings by MIT biologists.

Researchers shed light on shrinking of chromosomes

Jun 11, 2007

A human cell contains an enormous 1.8 metres of DNA partitioned into 46 chromosomes. These have to be copied and distributed equally into two daughter cells at every division. Condensation, the shortening of chromosomes, ...

Recommended for you

User comments : 0

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.