This can be a bad or a good thing. A mutation is a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke. Mutations can occur during DNA replication if errors are made and not corrected in time. Mutations can also occur as the result of exposure to environmental factors such as smoking, sunlight and radiation.
Often cells can recognize any potentially mutation-causing damage and repair it before it becomes a fixed mutation. Mutations contribute to genetic variation within species.
Mutations can also be inherited, particularly if they have a positive effect. For example, the disorder sickle cell anaemia is caused by a mutation in the gene that instructs the building of a protein called hemoglobin. This causes the red blood cells to become an abnormal, rigid, sickle shape. However, in African populations, having this mutation also protects against malaria. However, mutation can also disrupt normal gene activity and cause diseases, like cancer.
Cancer is the most common human genetic disease; it is caused by mutations occurring in a number of growth-controlling genes. Figure 1. An illustration to show an example of a DNA mutation. Image credit: Genome Research Limited. A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. Mutations range in size; they can affect anywhere from a single DNA building block base pair to a large segment of a chromosome that includes multiple genes.
This causes the red blood cells to become an abnormal, rigid, sickle shape. However, in African populations, having this mutation also protects against Plasmodium. Malaria parasites are transmitted by female Anopheles mosquitoes.
The parasites multiply within red blood cells, causing symptoms including anaemia light headedness, shortness of breath, racing heartbeat , and other general symptoms such as fever, chills, nausea, flu-like illness, and in severe cases, coma and death.
However, mutation can also disrupt normal gene activity and cause diseases, like cancer Cancer is the most common human genetic disease; it is caused by mutations occurring in a number of growth-controlling genes. Related Content:. What is DNA? What is DNA replication? What is genetic variation? This type of mutation results in a shortened protein that may function improperly or not at all.
As a result, the protein made by the gene may not function properly. Small deletions may remove one or a few base pairs within a gene, while larger deletions can remove an entire gene or several neighboring genes.
The deleted DNA may alter the function of the resulting protein s. A duplication consists of a piece of DNA that is abnormally copied one or more times. This type of mutation may alter the function of the resulting protein.
A reading frame consists of groups of 3 bases that each code for one amino acid. A frameshift mutation shifts the grouping of these bases and changes the code for amino acids. The resulting protein is usually nonfunctional. Insertions, deletions, and duplications can all be frameshift mutations.
In biological systems that are capable of reproduction , we must first focus on whether they are heritable; specifically, some mutations affect only the individual that carries them, while others affect all of the carrier organism 's offspring , and further descendants.
For mutations to affect an organism's descendants, they must: 1 occur in cells that produce the next generation, and 2 affect the hereditary material. Ultimately, the interplay between inherited mutations and environmental pressures generates diversity among species.
Although various types of molecular changes exist, the word " mutation " typically refers to a change that affects the nucleic acids. One way to think of DNA and RNA is that they are substances that carry the long-term memory of the information required for an organism 's reproduction.
This article focuses on mutations in DNA, although we should keep in mind that RNA is subject to essentially the same mutation forces. If mutations occur in non-germline cells, then these changes can be categorized as somatic mutations.
The word somatic comes from the Greek word soma which means "body", and somatic mutations only affect the present organism's body. From an evolutionary perspective, somatic mutations are uninteresting, unless they occur systematically and change some fundamental property of an individual--such as the capacity for survival. For example, cancer is a potent somatic mutation that will affect a single organism's survival.
As a different focus, evolutionary theory is mostly interested in DNA changes in the cells that produce the next generation. The statement that mutations are random is both profoundly true and profoundly untrue at the same time. The true aspect of this statement stems from the fact that, to the best of our knowledge, the consequences of a mutation have no influence whatsoever on the probability that this mutation will or will not occur. In other words, mutations occur randomly with respect to whether their effects are useful.
Thus, beneficial DNA changes do not happen more often simply because an organism could benefit from them. Moreover, even if an organism has acquired a beneficial mutation during its lifetime, the corresponding information will not flow back into the DNA in the organism's germline. However, the idea that mutations are random can be regarded as untrue if one considers the fact that not all types of mutations occur with equal probability.
Rather, some occur more frequently than others because they are favored by low-level biochemical reactions. These reactions are also the main reason why mutations are an inescapable property of any system that is capable of reproduction in the real world.
Mutation rates are usually very low, and biological systems go to extraordinary lengths to keep them as low as possible, mostly because many mutational effects are harmful. Nonetheless, mutation rates never reach zero, even despite both low-level protective mechanisms, like DNA repair or proofreading during DNA replication , and high-level mechanisms, like melanin deposition in skin cells to reduce radiation damage.
Beyond a certain point, avoiding mutation simply becomes too costly to cells. Thus, mutation will always be present as a powerful force in evolution. So, how do mutations occur? The answer to this question is closely linked to the molecular details of how both DNA and the entire genome are organized. The smallest mutations are point mutations, in which only a single base pair is changed into another base pair. Yet another type of mutation is the nonsynonymous mutation, in which an amino acid sequence is changed.
Such mutations lead to either the production of a different protein or the premature termination of a protein. As opposed to nonsynonymous mutations, synonymous mutations do not change an amino acid sequence, although they occur, by definition, only in sequences that code for amino acids. Synonymous mutations exist because many amino acids are encoded by multiple codons. Base pairs can also have diverse regulating properties if they are located in introns , intergenic regions, or even within the coding sequence of genes.
For some historic reasons, all of these groups are often subsumed with synonymous mutations under the label "silent" mutations. Depending on their function, such silent mutations can be anything from truly silent to extraordinarily important, the latter implying that working sequences are kept constant by purifying selection.
This is the most likely explanation for the existence of ultraconserved noncoding elements that have survived for more than million years without substantial change, as found by comparing the genomes of several vertebrates Sandelin et al.
Mutations may also take the form of insertions or deletions, which are together known as indels. Indels can have a wide variety of lengths. At the short end of the spectrum, indels of one or two base pairs within coding sequences have the greatest effect, because they will inevitably cause a frameshift only the addition of one or more three-base-pair codons will keep a protein approximately intact.
At the intermediate level, indels can affect parts of a gene or whole groups of genes. At the largest level, whole chromosomes or even whole copies of the genome can be affected by insertions or deletions, although such mutations are usually no longer subsumed under the label indel. At this high level, it is also possible to invert or translocate entire sections of a chromosome, and chromosomes can even fuse or break apart.
If a large number of genes are lost as a result of one of these processes, then the consequences are usually very harmful. Of course, different genetic systems react differently to such events.
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