A frameshift variant occurs when there is an addition or loss of nucleotides that shifts the grouping and changes the code for all downstream amino acids. The resulting protein is usually nonfunctional. Insertions, deletions, and duplications can all be frameshift variants. Some regions of DNA contain short sequences of nucleotides that are repeated a number of times in a row.
For example, a trinucleotide repeat is made up of sequences of three nucleotides, and a tetranucleotide repeat is made up of sequences of four nucleotides. A repeat expansion is a variant that increases the number of times that the short DNA sequence is repeated.
This type of variant can cause the resulting protein to function improperly. Other chapters in Help Me Understand Genetics. Genetics Home Reference has merged with MedlinePlus. Learn more.
The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. What kinds of gene variants are possible? From Genetics Home Reference. Variant types include the following: Substitution This type of variant replaces one DNA building block nucleotide with another. Missense : A missense variant is a type of substitution in which the nucleotide change results in the replacement of one protein building block amino acid with another in the protein made from the gene.
The amino acid change may alter the function of the protein. Nonsense : A nonsense variant is another type of substitution. Instead of causing a change in one amino acid, however, the altered DNA sequence results in a stop signal that prematurely signals the cell to stop building a protein.
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.
X-ray radiation is the kind used in X-rays medical images taken of teeth, bones, and other hard body parts. X-ray radiation has a very high energy level that can create molecules called free radicals. Free radicals are very unstable, and to become more stable, they can steal electrons from DNA, which can lead to mutations [ 5 ].
We can reduce exposure to X-ray radiation by using other forms of medical images when possible and wearing protective equipment to protect the body when x-rays are taken. If you have ever gone to the dentist and had an X-ray of your teeth, you probably remember having a heavy lead apron draped over your body. The lead apron protects the parts of the body that the dentist is not taking pictures of.
Getting X-rays only when necessary is a good practice to prevent any excessive negative effects on your DNA see Table 1 [ 5 ]. This is why X-rays are not taken if a doctor is fairly sure a patient has sprained, not broken, an ankle. How does smoking lead to cancer? Cigarettes and tobacco products contain chemicals referred to as carcinogens , which are mutagens that are also known to cause cancer.
All cancer cells have DNA mutations, and it is the carcinogens that cause the mutations. Carcinogens cause mutations by damaging the way the cell repairs DNA or makes proteins.
If the cancer cell is not able to repair this DNA damage, then it will keep dividing to make new cells and will pass the mutation on to all the new cells that are made. Because cancer cells grow and divide faster than normal cells, masses of these abnormal cells, called tumors, can form. The best way to avoid these carcinogens is not to smoke or use tobacco products see Table 1. It is also important to try to limit second-hand smoke exposure, which means avoiding other people who are smoking cigarettes [ 6 ].
Chemical mutagens are chemicals that have been shown to cause mutations. Some chemicals are also carcinogens and can cause cancer in humans, like the ones in cigarette smoke discussed above [ 2 ]. Some other examples of chemical mutagens include benzene a major component of gasoline , vinyl chloride common in pipes , and arsenic used in some insecticides and rat poison.
Some chemical mutagens have not been linked to cancer. To avoid mutations, we need to limit exposure to these chemicals by using protective equipment, like masks and gloves, when working with them. Once these chemicals are no longer being used, they should be properly disposed of see Table 1.
Substances called nitrites are present in many processed meats, such as bacon, pastrami, salami, hot dogs, and sausages. Nitrites combine with the proteins in the meat to form other compounds, which are known to be carcinogens [ 7 ]. Now I know what you are thinking: do I have to give up my favorite foods altogether?
Fortunately, the answer is no. You can still eat processed meats but eating them every day is probably not the best idea. To protect yourself from nitrites, you should limit your consumption of processed meats and also try to include healthy choices in your diet, like fruits, vegetables, and whole grains see Table 1. But sometimes they make no difference at all, or very little difference. Sometimes missense mutations cause amino acids to be incorporated, which make the protein more effective in doing its job.
More frequently, it causes the protein to be less effective in doing its job. But this is really the grist of evolution, when missense mutations happen, and therefore small changes, frequently small changes in proteins, happen, and it happens to be that it improves the function of a protein.
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