Important mutations in Visual Studio .NET

Creation QR Code in Visual Studio .NET Important mutations

Mutations occur all the time, but only certain mutations are important for evolution: those that are heritable For single-celled organisms like bacteria, all mutations are heritable A bacterium reproduces by dividing, and any changes that occur in the organism s DNA before division are passed on to the daughter cells That s not the case with animals Most of the cells in the human body, for example, don t contribute directly to the next generation Only the germ line (eggs and sperm) do, so only mutations in those tissues can be passed to offspring

Here s a major stumbling block many people have in understanding how mutations are involved in the process of evolution Many people think that

selectively advantageous mutations occur in response to environmental factors that make them advantageous The thinking goes this way: All these short-necked creatures are running around on the plains in Africa; their main food supply is the vegetation on the ground, but they eat so much, not enough ground vegetation is left to feed the population What do they do They evolve to have longer necks so that they can eat the leaves off the trees Voil ! Giraffes evolve, and the problem is solved But this scenario is absolutely not how evolution works Mutations don t occur in response to environmental factors; they already exist in the population In the presence of some new environmental factor that makes the mutation beneficial, the organism with that mutation is more likely to survive In the example of the short-necked creatures in Africa, suppose that a few random mutations result in a few long-necked individuals The long-necked ones and the short-necked ones still eat the rapidly diminishing grass supply, but the long-necked ones have an advantage because, in addition to grass, they can eat the leaves off trees Being better fed, they are more likely to survive and reproduce This principle that the mutation already exists in the population is crystal clear when you witness evolution in progress, which is possible with organisms that have short generational time spans Take a flask of bacteria, for example; put in some penicillin; and you re left with a flask that contains only a few surviving bacteria, all of which are penicillin resistant What happened Some of the bacteria in the flask already had slightly different DNA sequences that made them resistant to penicillin Examples illustrating the evolution of antibiotic resistance come up several times in this book because they so beautifully illustrates how organisms both simple and complex evolve Variation needs to exist in a population before the evolutionary forces can select for it Once the new selective force (climate change, new disease, and so on) appears, it s too late for any new mutations to be beneficial Only individuals that already have characteristics that are beneficial in the presence of the new selective force will have an advantage

A mutation is simply any change in the DNA sequence As you can imagine, more than one type of change is possible At each position in the DNA sequence, there are one of four possible nucleotides (A, C, T, and G) The simplest change to imagine is a change where the original nucleotide in a particular position is replaced by one of the other three possibilities An A is changed to either G, T, or C, for example Mutations of this type involving just a single point in the DNA sequence are called point mutations More complicated changes are also possible Whole sections of DNA can be removed, moved from one place to the

next, or duplicated The following sections explain these types of mutations in more detail (head to 15 for information on the significance of gene duplication) DNA is a long string of four different nucleotides that thread off in groups of three The different three-base sequences instruct the cell to assemble different amino acids into a protein Some three-base sequences instruct the cell where to start along the DNA sequence and where to stop Not all sections of an organism s DNA are used to code for proteins, but for the purposes of this discussion the important sections are those that do code for proteins (Refer to 3 for more detail about how the sequence of the DNA is used to code for the specific amino acids needed to make a given protein and 15 if you want to know more about non-coding DNA)