Gene Families

Gene families originate through gene duplication events during cell division, where mistakes cause DNA regions containing coding sequences to be duplicated. These duplicated gene copies, freed from constraints to maintain the original function, can acquire mutations and evolve new functions. Over time, groups of these related genes form gene families sharing common ancestry and similar sequences.

Paralogs are genes within the same species that evolved from a common ancestral gene through duplication. Orthologs are genes in different species that arose from a common ancestor but continued evolving after speciation events. Both are types of homologous genes, but paralogs represent duplication within a species, while orthologs represent divergence across species.

Duplicated genes can evolve faster because they are freed from selection pressure to maintain function. The original gene must preserve its sequence to sustain its essential role, but gene copies have no such constraint. This allows duplicated genes to accumulate mutations at a relatively faster rate and potentially develop novel functions.

Hemoglobin and myoglobin are related proteins in mammals that evolved from a common ancestral gene. Both perform oxygen binding but have specialized roles: hemoglobin functions as a primary oxygen transport molecule, while myoglobin specializes in oxygen storage. Their functional divergence demonstrates how duplicated genes within a gene family can evolve distinct roles.

A gene superfamily is a very large group of genes displaying enough homology to share common ancestry, often grouped by mechanistic similarities rather than strict sequence similarity. Gene families are smaller, more closely related groups. The immunoglobulin superfamily exemplifies this, comprising numerous genes coding for immune proteins sharing a common immunoglobulin fold domain.

Gene families can aid in hypothesizing the function of newly discovered genes by examining sequence similarity to known family members. Because genes within one family typically produce proteins performing similar functions, identifying a new gene's family membership and comparing its sequence to characterized homologs provides clues about its likely biological role.

Sequence similarity is a key tool for identifying and classifying gene families when examining genome sequences. Homologous genes within a family exhibit high sequence similarity due to their shared evolutionary origin. This similarity allows researchers to group related genes together and infer their common ancestry, even when studying newly sequenced genomes.