fastevolving

Fastevolving refers to genetic sequences or lineages that accumulate substitutions at a higher-than-average rate over time. In comparative genomics, fast-evolving elements may be identified among protein-coding genes, regulatory regions, or noncoding sequences, and they often point to rapid genetic change in response to selective pressures or relaxed constraints.

Causes of fast evolution include positive selection driving advantageous changes, relaxation of functional constraints that allows more mutations to persist, and intrinsic mutational biases or high recombination rates. Demographic factors such as population bottlenecks or expansions can also influence apparent rates by altering the fixation process. The result can be concentrated bursts of change in particular genes or regions, sometimes linked to environmental shifts, host–pathogen interactions, or reproductive biology.

Detection and measurement typically rely on comparing substitution rates. In coding sequences, researchers use the ratio of non-synonymous to synonymous substitutions (dN/dS) to infer selection or speed of evolution. In noncoding regions, rates are assessed relative to local neutral references or using models that account for rate variation across sites and lineages. Challenges include sequence saturation, alignment errors, and distinguishing selection from mutational bias.

Examples often cited include immune system genes such as those involved in pathogen recognition, sensory receptor genes, and certain reproductive genes, as well as rapidly evolving viral genomes. Fast-evolving regions can illuminate adaptive processes but may complicate phylogenetic reconstruction and molecular clock estimates due to rate heterogeneity.

See also: molecular clock, dN/dS, positive selection, rate heterogeneity.