Image Description: In the Phylogenetic Tree of Life, LUCA, an acronym for Last Universal Common Ancestor, is a population of ancestral organisms representing the hypothetical organism from which all current living organisms descend.
Life is a physico-chemical process from which living organisms originate.
The Phylogenetic Tree of Life is a model that illustrates the evolutionary relationships between different living species. This visual representation is essential in biology for understanding how species are connected to each other through common ancestors.
Phylogeny is the study of the evolutionary history and relationships among organisms. Phylogenetic trees are used to represent these relationships in the form of branching diagrams. The nodes of these trees represent common ancestors, while the branches represent evolutionary lineages.
Evolution is the process by which species change over time through natural selection, mutation, genetic drift, and other mechanisms. Species that share a recent common ancestor are closer on the phylogenetic tree than those that share a more ancient common ancestor.
The integration of DNA, RNA, and protein sequences into phylogenetic studies has transformed our understanding of evolutionary relationships. Their use allows the construction of more accurate phylogenetic trees, exploration of evolutionary mechanisms with fine resolution, and application of this knowledge to various fields, from evolutionary biology to medicine. Thanks to technological advances in sequencing and bioinformatics analysis, researchers can now study biological diversity on an unprecedented scale, revealing the complex links that unite all forms of life on Earth.
In phylogenetic data, scientists seek the tree that requires the fewest evolutionary changes.
They calculate the genetic distance between pairs of species and construct a tree based on these distances. Genetic distance is a measure of the divergence between the DNA, RNA, or protein sequences of different species. It quantifies the differences accumulated over time due to mutations and other evolutionary mechanisms.
Once the distances are calculated for each pair of species, they are organized into a distance matrix. Each element of this matrix represents the genetic distance between two species. Suppose we have three species A, B, C already aligned.
Species A: ATCG
Species B: ATGG
Species C: TTGG
Distance A-B: 1 (one substitution: C → G)
Distance A-C: 2 (two substitutions: A → T and C → G)
Distance B-C: 1 (one substitution: A → T)
| Matrice de distance | |||
| A | B | C | |
| A | 0 | 1 | 2 |
| B | 1 | 0 | 1 |
| C | 2 | 1 | 0 |
The closest pair is A and B with a distance of 1. Group A and B into a cluster, then calculate the distance from this cluster to C. The new distance is the weighted average of the distances: (2+1)/2=1.5. The resulting tree shows that A and B are closer to each other than they are to C.
The phylogenetic tree can be rooted or unrooted. A rooted tree shows the direction of evolution, indicating the last common ancestor. A monophyletic group, or clade, includes a common ancestor and all its descendants. These groups are crucial for understanding evolutionary relationships and species classification.
The robustness of phylogenetic trees is often assessed by bootstrap techniques, where the data are resampled to estimate the stability of the branches. Congruence analyses with independent data sets also strengthen confidence in inferred trees.
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