Gene Families

As cells are frequently dividing, they must also be frequently duplicating their genomes. During this process, mistakes can occur which lead to regions of DNA being duplicated. 

If a duplicated section of DNA contains one or more coding regions, this is referred to as gene duplication. Freed from the constraints placed on the original gene to maintain function, the gene copy can now acquire mutations and may evolve to fulfill a new function within the cell. We refer to genes which have evolved in this manner - through duplication of existing genes in the genome of a single species - as “paralogs”. 

Orthologs, on the other hand, is a term used to describe genes in different species that arose from a common ancestor but continued to evolve after one or more speciation events. 

The term “homolog” may be applied in both instances, and simply describes genes with a common ancestor. Groups of homologous genes are collectively referred to as “gene families”.

Because of their related DNA and resulting protein similarities, genes within one gene family typically produce proteins which perform similar functions. 

For example, hemoglobin and myoglobin are related proteins which both perform oxygen binding in mammals. However, hemoglobin has evolved as a primary oxygen transport molecule, whereas myoglobin’s role is in oxygen storage.

When examining genome sequences, such gene families can often be identified and classified due to their high sequence similarity. 

Additionally, studying gene families can aid in hypothesizing the function of a newly discovered gene even in the absence of a protein.