Sublineage

Sublineage is a term used in evolutionary biology and virology to describe a lineage that is nested within a broader lineage, representing a more recent branch on the evolutionary tree. In a phylogenetic context, a sublineage shares a recent common ancestor with its parent lineage but has diverged enough to be distinguished by unique sets of mutations. The concept fits within the hierarchical classification of lineages and clades used to summarize relationships among organisms or viral genomes.

In practice, sublineages are defined using genomic data and phylogenetic analysis. They are identified when a population accumulates characteristic mutations and forms a distinct, coherent cluster that can be traced back to a parent lineage. Sublineages help scientists track evolution, transmission patterns, and the emergence of phenotypic changes, such as altered transmissibility or antigenicity in viruses.

In the context of SARS-CoV-2, for example, the Omicron lineage has produced multiple sublineages, including BA.1, BA.2, BA.4, BA.5, and their descendants. Public health surveillance often reports data at the sublineage level to monitor which branches are circulating and whether they differ in clinical impact or vaccine sensitivity. However, sublineages are defined by genetic relationships rather than by a fixed set of traits, and definitions can shift as new data become available.

See also: phylogeny, lineage, clade, PANGO nomenclature, evolutionary biology.