Duplicating genes: A gene is born in .NET framework

Creator QR Code in .NET framework Duplicating genes: A gene is born

Errors in DNA replication can lead to duplications of sections of DNA or, as in the creation of polyploids, duplication of the entire genome (see 4) It s akin to going to Kinko s for a single copy and ending up with two: the copy you needed and an extra you re not quite sure what to do with The same thing goes for the DNA What s an extra gene good for If a mutation knocks out a duplicate copy, the organism is pretty much back where it started: It still has the original copy and an extra This situation is the spare-tire gene duplication theory (Just kidding) The extra copy may or may not be functional: When the second copy is nonfunctional: These nonfunctional genes are called pseudo-genes Pseudo-genes look like the original genes, but they re a little, or a lot, broken, and they tend to accumulate more and more mutations over time The more mutations occur, the harder it is to recognize that these genes are related to existing genes But since they re already nonfunctional, there s no fitness cost to a few more mutations When the second copy is functional: If the second copy mutates such that it is able to perform an additional function that s selectively advantageous, individuals with this mutation increase in frequency, resulting in two different yet related functional genes where one originally was Many examples exist of families of genes that appear to have a common ancestor When you know about the possibility of gene duplications, you understand that natural selection could result in a change of function of one copy without having to worry about losing the function of the other copy When you have two copies, you have room to move Because most mutations are deleterious, these duplicated genes usually end up losing their original function without acquiring any new function But sometimes beneficial mutations occur in the second copy, and a new gene is born

The neutral theory of molecular evolution says that genetic drift random events that affect evolutionary change (see 6) accounts for much of the change in DNA This is the case because most mutations are selectively neutral In fact, much more variation is neutral than scientists once thought The variation exists in the DNA, but either it doesn t result in a change at the level of the protein or, if it does result in changes in proteins, these changes don t change the protein s function The chance that a mutation will have no effect can vary between different genes Some proteins, for example, are very tightly constrained in the shapes that they can adopt and still be functional For these proteins, relatively few mutations are selectively neutral When scientists examine the mutation rates of different proteins within the same organism, they find that some evolve faster than others As stated previously, neutral mutations are neither good nor bad, and when a mutation is neutral, natural selection doesn t act on it (Why should it A neutral mutation doesn t help the organism, which would cause an increase in frequency in subsequent generations Neither does it hurt the organism, which would cause a decrease in frequency) Therefore, the evolutionary force that acts on these genes is genetic drift Over enough time, a selectively neutral mutation can reach a frequency of 100 percent in a population just by chance a situation called fixation (You can read more about fixation and genetic drift in 6) Many mutations are almost, but not quite, neutral A slightly deleterious mutation, for example, might still increase in frequency as a result of genetic drift in a small population Remember that for any given mutation, the chance of fixation (that is, the chance of reaching a frequency of 100 percent) is a function of population size If population size fluctuates (as it often does), a particular gene may be changing in frequency primarily as a result of natural selection at one time and primarily due to genetic drift at another time Two evolutionary forces are at work: natural selection and genetic drift If a mutation isn t neutral, both natural selection and genetic drift can be the cause of evolution If a mutation is neutral, only genetic drift can result in a change in the frequency of the gene over time (This discovery that random events are evolutionary forces in and of themselves has been the most important addition to the theory of evolution since Darwin)