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Orthology refers to traits inherited from a common ancestor, while evolutionary analogy refers to traits that evolved independently. Orthologous genes are passed on intact, resulting in similar physical traits. Orthology is important for comparing gene function and classifying life on Earth.
An orthology is a trait in two or more species that has been inherited from a common ancestor. It can be contrasted with an evolutionary analogy, which is a similar trait that evolved independently. Genes passed on from parents to offspring may remain intact, which will often result in the display of similar physical traits. If genes mutate many times, however, they can end up producing similar outward traits through natural selection. Orthology in different species refers to similar traits whose genes have an inherited, rather than a mutated, origin.
Different species exhibit different characteristics, but some of these traits can be very similar. For example, many animals have hands with five fingers, although these fingers can vary significantly in size or shape. Orthology concerns the origin of genes responsible for physical traits such as fingers. These genes can evolve in two different ways: independently through mutation or heritably through orthology.
Nature is full of examples of traits that evolved independently. For example, both sharks and dolphins have streamlined bodies with a vertical fin on their backs. The internal anatomy of sharks and dolphins, however, is very different; in fact, they are evolutionarily quite distant. Their closest common ancestor lived long in the past. Rather than being inherited, the genes responsible for many of their similar traits evolved independently due to their similar environment.
Closely related species, on the other hand, inherit many of the same traits from a common ancestor. When this happens, the templates in a deoxyribonucleic acid (DNA) molecule are passed on to offspring intact for many generations. Without any mutations to alter the genes, they will be inherited by the offspring and often result in the same external traits as the ancestor organisms. If heredity is the cause of a particular gene, it is said to be orthologous.
When an orthology occurs, the gene in question may or may not have the same function in the life and reproduction of its host. In many cases, the gene will play the same role. Fingers in primates, for example, typically have similar functions: picking up food, moving through trees, and fighting enemies. However, orthologous genes will occasionally play different roles. Humans have five fingers, but cannot grip branches like a gorilla’s fingers.
Identifying the orthology is critical for comparing gene function across organisms. It is also helpful in classifying life on Earth, which is called taxonomy. Knowing the origins of particular genes can help scientists understand why some animals, such as sharks and dolphins, look similar but behave very differently.
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