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+Identifying  core genes  is important  to understand  evolutionary and
+functional phylogenies. Therefore, in  this work we present methods to
+build a genes  content evolutionary tree. More precisely,  we focus on
+the following  questions considering a  collection of 99~chloroplasts
+annotated from NCBI \cite{Sayers01012011} and Dogma \cite{RDogma}: how
+can  we identify the  best core  genome and  what is  the evolutionary
+scenario of these chloroplasts.\\
+Chloroplast (such as mitochondria) are fondamental key elements in 
+living organisms history. Indeed, chlorplast in Eucaryotes are organites responsible for 
+photosynthesis. Photosynthesis is the main way to produce organic matter 
+from mineral matter, using solar energy. Consequently photosynthetic 
+organisms are at the base of most ecosystems trophic chains and 
+photosynthesis in eucaryotes allowed a great speciation in the lineage 
+(to a great biodiversity). From an ecological point of view, 
+photosynthetic organisms are at the origin of the presence of dioxygen 
+in the atmosphere (allowing extant life) and are the main source of mid- 
+to long term carbon stockage (using atmospheric CO2, important in the 
+context of climate change). Chloroplast found in Eucaryots have an endosymbiotic origin, meaning 
+that they are a fusion of a photosynthetic bacteria (Cyanobacteria) and 
+a eucaryotic cell (enable to produce organic matter = heterotrophic). 
+This fusion or First Endiosymbiosis ended in a Great diversification of 
+a lineage comprising Red Algae, Green Algae and Land Plants (terrestrial).
+Several Second Enbiosymbioses occurred then: two involving a Red 
+Algae and other heterotrophic eucaryotes and giving birth to both Brown 
+Algae and Dinoflagellates lineages; another involving a Green Algae and 
+a heterotrophic eucaryot and giving birth to Euglens.
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