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Genomic selection, an important method based on simple priniciples

Genomic selection consists in establishing statistical relations between the genotype of an animal, that is all its genes or more exactly, the alleles of its genes, and the value observed of one or more important traits (1), like for example in dairy cows, the quantity or quality of milk, or mastitis resistance.

Thus, it is just necessary to determine the genotype of an individual to deduce its potential for a specific trait: a simple DNA analysis at birth, without waiting for the individual to grow. Considerable time is thus gained for the testing of reproducing animals and their descendants in selection schemes.

Genomic selection is based on three conditions:

• the existance of a sufficiently big reference population presenting a polymorphism for the trait that we are interested in in order to establish solid statistical relations between gentoype and phenotype. 
• high throughput genotyping capacity
• high throughput phenotyping capacity

New selection criteria are available

The use of genomics selection will meet increasingly complex selection objectives and will combine health, quality and sustainability traits. These traits are becoming accessible thanks to phenotyping progress. For dairy cattle for example, we can now easily determine and at a low cost the fine composition of milk (2), using a high-throughput spectrometry method (3). Dairy robots are important systems of observation of animals allowing the collection of different data: milk analysis, milk flow, animal weight ....

We also intend on characterizing the traits responsible for animal health: mastitis or paratuberculosis susceptibility.

Feed efficiency (the quantity of food ingested, quantity of waste) is also an important trait to be explored since animal feeding is one of the highest costs.

The challenge: a reference population

Genomic selection is based on the availability of a reference population which should be genetically similar to the breeding animals we want to test (4). This population should also include individuals living under different environments to avoid selecting animals that will perform well in one given environment but not in other environments, and to minimize the genotype/environment interactions.

The exchange of data on these populations will probably induce new types of organization in order to conserve investors' interests while facilitating the mutualization to improve cost sharing. National organization that currently exists for ruminants could also be expanded internationally.

Currently developed for dairy cattle, genomic selection will be applicated in all species to different degrees depending on its economic interest. This will be greater with longer generations, more valued breeding animals and difficult or costly phenotyping.

^{(1)  The expression of a complex trait often depends on several genes: these genes vary as a function of the combination of alleles of these genes that are present in the genotype that is studied. This combination is characterized in genomic selection, by the variation of SNP markers (Single Nucleotide Polymorphism), simple polymorphisms made up of the substitution of a nulceotide by another). An SNP profile is also linked to the level of the expression of a trait without needing to identify the genes implicated.} 

^{(2)  Fatty acid, fat and protein compositions.}

^{(3)  Middle Infrared Spectrometry (MIR).}

^{(4)  Ideally including the candidates' parents generation.}

… To find out more : http://www.inra.fr/Chercheurs-etudiants/Systemes-agricoles/Toutes-les-actualites/Regards-d-expert-Quelle-vache-pour-demain