Relative apparent synapomorphy analysis, or RASA, is a method that aims to determine whether a given character is shared between

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

due to shared ancestry or due to

convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that ...

. A

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

is a shared trait found among two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. RASA assigns a score to the character based on its potential to be informative.

Limitations

The method performs poorly when used to select an outgroup taxon, to quantify the amount of

phylogenetic signal In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

present, or to identify taxa that may be prone to

long branch attraction In phylogenetics, long branch attraction (LBA) is a form of systematic error whereby distantly related lineages are incorrectly inferred to be closely related. LBA arises when the amount of molecular or morphological change accumulated within a lin ...

References

Taxonomy (biology) {{biology-stub