The original question was:
I was wondering, has there ever been a documented mutation that produced a completely brand new function in an organism that wasn’t there before. I know that there have been a very small amount of beneficial mutations, but every example I’ve seen involves getting something broken.
Answer by Diane Eager
Since any function in a living organism results from the coordinated actions of many interrelated genes, the task of gaining a new function that did not exist before, requires changes to produce many new genes, as well as alterations in their many ‘control genes’ which would switch such ‘new’ genes on and off in order to make them work with the rest of the organism’s ‘original’ genes. So the first point should be obvious: no single mutation could ever produce a whole new function or structure that did not exist before as mutations can only modify what already exists.
The closest observed changes that fit the concept of a “brand new function” are mutations found in some bacteria that enable them to digest chemicals they didn’t feed on before. The two best known of these are bacteria that can feed on components of nylon, which is a man-made substance, and bacteria that began to feed on citrate when oxygen was present, when previously they only fed on citrate in the absence of oxygen.
However, a close study of these “gain of function” mutants, reveals they also involve variation and/or degeneration of existing functions, rather than something that has never existed before. Let me explain.
Nylon Eating Bacteria
No – these will not produce holes in your stockings, or eat your fishing line. They are bacteria that were found living in the waste water flowing from a nylon factory. They were not digesting fully formed nylon threads, but the chemical components that are used to manufacture nylon.
This is not as strange as it seems. Nylon is made of multiple strings of carbon based molecules. The basic components used to make nylon are derived from coal and oil, which are originally derived from decayed carbon rich organic matter, e.g. buried trees and dead dinosaurs. Many molecules in living things are also long strings of carbon based molecules, so the kind of cellular machinery needed to break them down could, with a little tweaking, potentially break down any long strings of carbon based molecules, including the components of nylon – and that is what happened. An enzyme that already existed in the bacteria became mutated so its shape became deformed, and its function became less specific. What does this mean?
An enzyme is a molecule that facilitates and regulates certain chemical reactions in a cell. To do this the enzyme has a very specifically shaped cleft, or indentation, into which the reacting chemicals fit which makes the reaction easier and faster. Without the enzyme, the reaction can occur, but it usually takes either a lot longer or needs much higher temperatures, both of which can be fatal to life. Since the enzyme’s shape is determined by gene instructions, any small mutation in the gene may produce a change in the shape of the cleft, which can allow other molecules that are not normally involved in that enzyme’s reaction to also fit in the ‘hole’, and therefore be involved in any chemical reaction controlled by that enzyme. In the case of nylon bacteria, a change in an enzyme shape enabled carbon based nylon components to fit into it, and the enzyme broke them down into smaller molecules that the bacteria could then use for food.
Is there a limit to how much enzyme tweaking can occur? Yes. If the enzyme cleft becomes two large or misshapen it becomes useless and no reaction occurs.
We have previously been asked about the citrate bacteria. See answer to the question: Bacteria Evolution: Lenski’s E coli experiment. Has it shown bacteria can evolve new information? Answer here.
Mutations and New Functions
Changing functions by mutations is the equivalent of firing a bullet through a complicated machine. It may hit a component, and this may modify its structure and function, but this will not improve it or give it completely new function it didn’t have before. It may knock a component slightly askew, allowing the machine to still function, but most times it will render it useless. This is why mutations are associated with disease and degeneration, rather than improving living things, and why people quite rightly avoid situations that produce mutations, such as radiation and some chemicals.
Ultimately, the only way to get a new function into a living organism is by genetic engineering, i.e. deliberately inserting a whole new gene into an organism that did not have it before. Even then it doesn’t always work because genes do not function in isolation. They have to work with other genes in the cell and be activated and deactivated at the right time and in the right place. Furthermore, gaining functions by genetic engineering is the opposite of evolution. Genetic engineering requires intelligent scientists to find the gene for a function and deliberately insert it into another living cell by skill manipulation. Random mutations can never do this.
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