Ohnologs

Ohnologs are genes or DNA sequences that are the result of a whole-genome duplication event. The term "ohnolog" is derived from "homolog," meaning similar genes, and "ohno," referring to Susumu Ohno, a geneticist who first proposed the significance of whole-genome duplication in vertebrate evolution. When an organism undergoes a whole-genome duplication, its entire set of genes is essentially copied. After this event, the duplicated genes are called ohnologs.

Over evolutionary time, these duplicated genes can follow several paths. Some may remain redundant and continue to perform the same function. Others might diverge slightly, acquiring new, but related, functions. A third possibility is that one copy of the gene is lost entirely, reverting to a single-gene state. In some cases, one copy may become a non-functional pseudogene. The study of ohnologs is crucial for understanding genome evolution, gene duplication, and the development of new biological functions.

Ohnologs are particularly prevalent in the genomes of certain organisms, most notably in vertebrates, where multiple rounds of whole-genome duplication are thought to have occurred early in their evolutionary history. Identifying and analyzing ohnologs helps scientists reconstruct evolutionary relationships between species and understand the genetic basis for the diversification of life. The presence and pattern of ohnologs can serve as molecular clocks or markers for ancient evolutionary events.