How can mutations be helpful

Notwithstanding the doubters, Houseley and his team are persevering with their research to understand its relevance to cancer and other biomedical problems. He thinks that chemotherapy drugs and other stresses on tumors may encourage malignant cells to mutate further, including mutations for resistance to the drugs.

If that resistance is facilitated by the kind of mechanism he explored in his work on yeast, it could very well present a new drug target. Cancer patients might be treated both with normal courses of chemotherapy and with agents that would inhibit the biochemical modifications that make resistance mutations possible. This article was reprinted on Wired.

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Mutations are changes in the genetic sequence, and they are a main cause of diversity among organisms. These changes occur at many different levels, and they can have widely differing consequences. 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. The most common cause of CMT1 is a duplication of part of chromosome A point mutation is a change in a single nucleotide in DNA.

This type of mutation is usually less serious than a chromosomal alteration. Point mutations can be silent, missense, or nonsense mutations, as described in Table 5. The effects of point mutations depend on how they change the genetic code. A frameshift mutation is a deletion or insertion of one or more nucleotides, changing the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides.

Consider the following sequence of bases in RNA:. Now, assume that an insertion occurs in this sequence. The sequence of bases becomes:. Even though the rest of the sequence is unchanged, this insertion changes the reading frame and, therefore, all of the codons that follow it. As this example shows, a frameshift mutation can dramatically change how the codons in mRNA are read. This can have a drastic effect on the protein product. The majority of mutations have neither negative nor positive effects on the organism in which they occur.

These mutations are called neutral mutations. Examples include silent point mutations, which are neutral because they do not change the amino acids in the proteins they encode. Many other mutations have no effects on the organism because they are repaired before protein synthesis occurs. Cells have multiple repair mechanisms to fix mutations in DNA.

Some mutations — known as beneficial mutations — have a positive effect on the organism in which they occur. They generally code for new versions of proteins that help organisms adapt to their environment. There are several well-known examples of beneficial mutations. Here are two such examples:. Imagine making a random change in a complicated machine, such as a car engine. There is a chance that the random change would result in a car that does not run well — or perhaps does not run at all.

Such mutations are likely to be harmful. Harmful mutations may cause genetic disorders or cancer. Inherited mutations are thought to play a role in roughly five to ten per cent of all cancers. Specific mutations that cause many of the known hereditary cancers have been identified. Most of the mutations occur in genes that control the growth of cells or the repair of damaged DNA.

Genetic testing can be done to determine whether individuals have inherited specific cancer-causing mutations. Some of the most common inherited cancers for which genetic testing is available include hereditary breast and ovarian cancer , caused by mutations in genes called BRCA1 and BRCA2. Besides breast and ovarian cancers, mutations in these genes may also cause pancreatic and prostate cancers. This specific sequence change is the mutation found in most people with sickle cell anemia, which is a very painful condition.

Other times, a base is inserted into or deleted in the DNA sequence, which alters the way codons are read. This results in a large number of amino acids being altered, which is called a frameshift mutation. Notice how none of the amino acids in the protein made from the mutated DNA are the same as the original sequence. A third possibility is that the mutated DNA sequence causes the protein production to stop early, so that the protein is shorter than normal.

This is referred to as a nonsense mutation. So, the resulting protein would be shorter than normal and would not function properly. Mutations can be passed down from the mother or father to the developing baby, and these are called inherited mutations. For example, if your mother had a mutation that caused her to be a lot shorter than average, you could inherit her mutation and be shorter than average yourself. If a person with an inherited mutation has a baby one day, that person would pass the mutation on to the next generation.

With the example above, if you gave your son or daughter the short stature mutation your mom gave you, your child could say he is short because of both you and his grandmother your mother.

Other mutations happen after birth, and these are called acquired mutations. Acquired mutations are usually due to something in the environment and their effects are usually only present in the cells that were exposed to that environmental trigger. So, some cells will have the mutation and other cells will have the normal sequence.

For example, if you somehow got a mutation in the skin cells on your knee and then scraped your knee and had to make new cells to replace the ones that got hurt, those new cells would contain the mutation. However, the mutation would not be passed on to your future offspring, if you had a baby later. Sunlight is one thing that can cause mutations. How does sunlight affect our DNA?

Sunlight creates structures called thymine dimers , which means that two thymine T bases T on the same DNA strand become connected in an abnormal way, instead of correctly attaching to the complementary base adenine A on the opposite strand. Thymine dimers create kinks in the DNA shape see Figure 3 [ 2 ]. These kinks make DNA difficult to copy, which can cause a mutation. In order to avoid thymine dimers from developing in our cells, it is very important to use sunscreen to help block ultraviolet A and B UVA and UVB rays.

Sunscreen should be reapplied every 2 h or after swimming, sweating, bathing, or using a towel [ 4 ]. Some individuals who have especially sensitive or light skin should consider higher levels of UV protection and are encouraged to consult a doctor called a dermatologist, who is an expert on keeping skin healthy.