What do mutations cause

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. 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. 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? What types of mutation are there? They determine our traits, which are things like hair color, height, body type, and other things that make a person unique.

Genes also play a role in a person's risk for some diseases and health conditions. Each of us has about 24, different types of genes. DNA deoxyribonucleic acid is the carrier of all our genes. Each person gets one copy of DNA from their mother and one copy from their father. This code determines which genes a person has. DNA is located inside the chromosomes. A chromosome KRO-muh-sohm is an X-shaped thread-like structure in the body's cells.

To be extra certain that they were detecting brand new mutations, they focused on genome positions where the child was a heterozygote and both parents were homozygotes. They then checked their data using several different methods. After all, primates are diploid ; if a primate offspring shows up with a mutation on one chromosome out of a pair, how do we tell which chromosome, the one from the egg or the one from the sperm, contributed that mutation? Figuring it out requires looking at nearby positions on the chromosome — i.

If the new mutation is located on a chromosome near a signature sequence present only in the genetic father, we know that person must have contributed the mutation. Teachers can use the following resources to build a lesson sequence around mutation, genetic variation, and evolution for the high school or college levels. For answer keys to the worksheets above, teachers can email UEKeys berkeley.

The following Data Nugget activities for middle and high school students offer opportunities to analyze data on mutation, reproductive cells, genetic variation, and evolution:. Wu, F. PLoS Biol. The effects of mutations. Gene flow. Subscribe to our newsletter. Email Facebook Twitter. Mutations happen for several reasons. That small difference from the original DNA sequence is a mutation.

Spontaneous breakdown of DNA can also cause mutations. External influences can cause mutations Mutations can also be caused by exposure to specific chemicals or radiation that cause the DNA to break down. Whatever the cause, mutations occur any time a cell ends up carrying a DNA sequence slightly different than the original.