A Simple Genetic Mechanism May Be Behind The Origin Of Species
France - How to create reproductive barriers that isolate species from each other? A study conducted by the team of Olivier Loudet, INRA Versailles in collaboration with the University of Nottingham, revealed one aspect of their introduction into the genome during evolution.

Specializing in the genetic model plant Arabidopsis thaliana, the researchers first found that the offspring of cross between two natural strains of the plant-Columbia (Col) and Cape Verde Island (CVI) - not entirely obeyed classical laws of heredity: some individuals resulting from specific genetic combination of the two parental genomes were missing.

They discovered that this phenomenon resulted from an incompatibility between two chromosomal regions, carried on chromosome 1 and chromosome Col. 5 of CVI, which never found together in the homozygous state in the genome of plants from their intersection .

A genetic study further allowed them to attribute this inconsistency to a single gene, one of histidinol phosphate aminotransferase (HPA): it is carried by chromosome 1 in strain CVI and is present in two copies on chromosomes 1 and 5, in strain Col.

Inactivation during the evolution of the copy of this HPA on chromosome 1 of Col has meant that, in Arabidopsis, the functional gene is carried by a different chromosome in CVI and neck. But the HPA gene encodes an enzyme essential for the synthesis of histidine, an essential amino acid: the descendants of these two strains that inherit both the HPA inactive gene carried by chromosome 1 of Col chromosome 5 and CVI can not grow, private HPA functional gene.

Evidence that the absence of this gene is the cause of the inconsistency observed chromosome, researchers found that these embryos developed normally if the plants that bore them were sprayed with a solution containing histidine.
"The fact that the progeny of certain crosses is not always fertile is known in almost all families of plants, says Olivier Loudet. But here, for the first time we've pinpointed a simple mechanism that this explains in a species. "
Duplication and fragmentation of essential genes in the genome, followed by inactivation of some copies of these genes during evolution could gradually reduce the possibilities of cross fertilization between different strains and eventually lead to their separation distinct species. This quick and simple mechanism could partly explain the genetic origin of species. These results are published in the journal Science on January 30, 2009.


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