gene families and pseudogenes
/ SOO-doh-jeen /
Genes are not all unique one-offs. Many come in families — sets of related genes that descend from a shared ancestor through duplication, like cousins who all carry a family resemblance. And alongside the working family members sit broken copies that look like genes but no longer make a functional product: pseudogenes, the relics of the process.
A gene family arises when a gene is accidentally duplicated and the copies drift apart over evolutionary time. The copies (called paralogs) keep enough similarity to be recognized as relatives but can specialize: the globin family, for instance, includes the genes for hemoglobin subunits expressed at different life stages and myoglobin in muscle. Pseudogenes form in two main ways: a duplicated copy accumulates disabling mutations (a stop codon, a frameshift) and stops working, or a processed messenger RNA is reverse-transcribed back into the genome lacking its promoter and introns, landing as a non-functional 'processed pseudogene'. The human genome holds well over ten thousand pseudogenes.
This matters because gene duplication is a primary route to evolutionary novelty: one copy can keep the original job while the other is free to mutate and perhaps acquire a new function, without leaving the organism short. Pseudogenes, once dismissed as dead, sometimes are not entirely silent — a few are transcribed into regulatory RNAs that influence their living relatives. Comparing family members and pseudogenes across species is also a powerful way to read genome history, much like reading edits and deletions in successive drafts of a document.
The human olfactory (smell) receptor genes form a huge family of about 800 members — but more than half are pseudogenes, broken by mutation, which is one reason our sense of smell is weaker than a dog's. The working members still let us distinguish a vast range of odours.
Gene families grow by duplication; pseudogenes are the broken copies left behind.
Pseudogene means 'looks like a gene but does not make a normal protein' — not always 'completely dead'. A minority are transcribed into RNAs that regulate their functional relatives, so 'pseudo' should not be read as 'totally inert'.