phylogenetisk

Phylogenetisk, or phylogenetic in English, is a branch of evolutionary biology that studies the relationships among organisms or genes based on their evolutionary history. It aims to reconstruct phylogenies—hypothetical trees that depict lines of descent from common ancestors. A phylogenetic tree shows nodes (ancestors), branches (lineages), and tips (the studied organisms or genes); branch lengths may reflect genetic change or time depending on the method used. Inference is based on data such as DNA, RNA, and protein sequences, as well as morphological or other characters.

Common methods include cladistics, which emphasizes shared derived characters to define monophyletic groups (clades); distance-based approaches; and model-based methods such as maximum likelihood and Bayesian inference. Data sources span genomic sequences, transcriptomes, proteomes, and, when available, fossil traits and morphological data. Key concepts include monophyly, paraphyly, and polyphyly; the use of outgroups to root trees; and the distinction between rooted and unrooted trees. The molecular clock hypothesis is sometimes used to relate genetic change to time.

Applications of phylogenetics include informing taxonomy to reflect evolutionary history, comparative biology, and the study of pathogen evolution and transmission. It also supports conservation decisions, biogeography, and studies of functional evolution. History-wise, Darwin proposed common descent, while Willi Hennig and later computational advances in the 20th century established modern phylogenetics as a rigorous, data-driven framework. Challenges remain, such as homoplasy (convergent traits), incomplete lineage sorting, horizontal gene transfer, and data gaps or model mis-specification. Phylogenetic analyses are continually refined as new data become available.