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L’arbre de la vie

Pour définir ces liens de parenté, les biologistes recherchent ce qui rapproche les espèces mais aussi ce qui les distingue, comme lorsqu’on observe un petit-fils et son grand-père. A l’image d’un arbre généalogique, ils récapitulent aussi ces liens de parenté dans un arbre: l’arbre de la vie.

A l’époque de Darwin, on commença par comparer les espèces sur la base de leur morphologie – la présence de poils ou d’écailles, le nombre de pattes ou, pour les plantes, la position des feuilles sur une tige, par exemple.

Using the leap in knowledge made in the field of biology combined with the deciphering of the genomes of different species, it is currently possible to estimate the degree of parenthood between all species by ‘reading’ their genes and proteins. What is more, the calculating power of computers and high-performance bioinformatics methods of analysis are able to compare simultaneously a great number of genes, or proteins, between many species – from bacteria to humans.

Universal proteins

All species living on earth share something very intimate: ribosomes. The proteins that make up ribosomes are essential to life since they are themselves involved in making proteins. Ribosome proteins are frequently used by bioinformaticians to construct phylogenetic trees. There are about 200 other ‘universal’ proteins.

The tree of life

…created by scientists who compared 31 families of universal proteins from 191 different species.

The 3 domains of life

Bacteria / Eubacteria (Prokaryotes)
Unicellular organisms; their DNA is not kept inside a nucleus.

Archaea / (Prokaryotes)
Unicellular organisms; their DNA is not kept inside a nucleus. Unlike bacteria, however, archaea generally live in extreme conditions (high acidity, high temperatures, high pressure, …).

Eukaryotes
Organisms whose cells have a nucleus which protects their DNA. It is the case of animals – humans included – plants and fungi.

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