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.
+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 from solar energy = heterotrophic). \\
+
+By the principle of
+classification, a small number of genes lost among species indicates
+that these species are close to each other and belong to same family,
+while a large lost means that we have an evolutionary relationship
+between species from different families.
