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Recommended for: Grades 9-12

Resource: Molecular Clocks: Proteins That Evolve at Different Rates

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Four different proteins from humans and horses are compared in this graphic and article, and the reasons each protein evolves at its own characteristic rate are discussed. Each protein is useful for measuring evolutionary change over a different time scale.

Teachers' Domain, Molecular Clocks: Proteins That Evolve at Different Rates, published September 26, 2003, retrieved on ,
http://www.teachersdomain.org/resource/tdc02.sci.life.evo.molecclocks/

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The basic mutation rate is probably similar for all genes, but natural selection filters out mutations that adversely affect the functioning of the protein each gene makes. The structure of some proteins is rigidly defined by the function they perform -- any mutation that causes even a small change in the molecular structure will impair the protein's function. These proteins accumulate very few mutations and may be identical in many species, which means they have limited use in working out how closely different species are related. Other proteins can tolerate a large amount of change and still carry out their function. Such proteins accumulate many mutations, and they can be used to help work out the evolutionary relationships between even closely related species.