A mutation is a change in the DNA sequence of an organism. Mutations can result from errors in DNA replication during cell division, exposure to mutagens or a viral infection. Germline mutations (that occur in eggs and sperm) can be passed on to offspring, while somatic mutations (that occur in body cells) are not passed on.
Mutation has been the source of many Hollywood movies, but it's really a simple process of a mistake made in a DNA sequence as it's being copied. Some of that's just the background noise that DNA copying is not perfect, and we should be glad of that or evolution couldn't operate. But mutation can also be induced by things like radiation or carcinogens in a way that can increase the risk of cancers or birth defects. But it's pretty simple; it's basically an induced misspelling of the DNA sequence. That's a mutation.
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.
An illustration to show an example of a DNA mutation.
Image credit: Genome Research Limited
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English naturalist Charles Darwin developed the idea of natural selection after a five-year voyage to study plants, animals, and fossils in South America and on islands in the Pacific. In 1859, he brought the idea of natural selection to the attention of the world in his best-selling book, On the Origin of Species.
Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable, meaning that they are all different in some ways. This variation means that some individuals have traits better suited to the environment than others. Individuals with adaptive traits—traits that give them some advantage—are more likely to survive and reproduce. These individuals then pass the adaptive traits on to their offspring. Over time, these advantageous traits become more common in the population. Through this process of natural selection, favorable traits are transmitted through generations.
Natural selection can lead to speciation, where one species gives rise to a new and distinctly different species. It is one of the processes that drives evolution and helps to explain the diversity of life on Earth.
Darwin chose the name natural selection to contrast with “artificial selection,” or selective breeding that is controlled by humans. He pointed to the pastime of pigeon breeding, a popular hobby in his day, as an example of artificial selection. By choosing which pigeons mated with others, hobbyists created distinct pigeon breeds, with fancy feathers or acrobatic flight, that were different from wild pigeons.
Darwin and other scientists of his day argued that a process much like artificial selection happened in nature, without any human intervention. He argued that natural selection explained how a wide variety of life forms developed over time from a single common ancestor.
Darwin did not know that genes existed, but he could see that many traits are heritable—passed from parents to offspring.
Mutations are changes in the structure of the molecules that make up genes, called DNA. The mutation of genes is an important source of genetic variation within a population. Mutations can be random (for example, when replicating cells make an error while copying DNA), or happen as a result of exposure to something in the environment, like harmful chemicals or radiation.
Mutations can be harmful, neutral, or sometimes helpful, resulting in a new, advantageous trait. When mutations occur in germ cells (eggs and sperm), they can be passed on to offspring.
If the environment changes rapidly, some species may not be able to adapt fast enough through natural selection. Through studying the fossil record, we know that many of the organisms that once lived on Earth are now extinct. Dinosaurs are one example. An invasive species, a disease organism, a catastrophic environmental change, or a highly successful predator can all contribute to the extinction of species.
Today, human actions such as overhunting and the destruction of habitats are the main cause of extinctions. Extinctions seem to be occurring at a much faster rate today than they did in the past, as shown in the fossil record.
A mutation is a change in the structure of a gene, the unit of heredity. Genes are made of deoxyribonucleic acid (DNA), a long molecule composed of building blocks called nucleotides. Each nucleotide is built around one of four different subunits called bases. These bases are known as guanine, cytosine, adenine, and thymine. A gene carries information in the sequence of its nucleotides, just as a sentence carries information in the sequence of its letters.
One type of mutation is a change in a base. This is called a point mutation and it is like changing one letter in a word. Most genes carry instructions for making proteins. When a base is changed in a gene, different results are possible, depending on which base is changed and what it is changed into. The gene may produce an altered protein, it may produce no protein, or it may produce the usual protein. Most mutations are not harmful, but some can be. A harmful mutation can result in a genetic disorder or even cancer.
Another kind of mutation is a chromosomal mutation. Chromosomes, located in the cell nucleus, are tiny threadlike structures that carry genes. A chromosome consists of a molecule of DNA together with proteins. Sometimes, a long segment of DNA is inserted into a chromosome, deleted from a chromosome, flipped around within a chromosome, duplicated, or moved from one chromosome to another. Such changes are usually very harmful.
One example of a chromosomal mutation is a condition called Down syndrome. In each cell, humans normally have forty-six chromosomes, consisting of two copies of the twenty-three kinds of chromosomes. Down syndrome usually results from the presence of one extra copy of a particular chromosome, or an extra portion of that chromosome. The presence of that extra chromosome leads to problems with certain organs of the body, such as the heart. It can also lead to leukemia—a cancer of the blood-forming cells—and produce mental disabilities. Many people with Down syndrome also have distinct facial features.
Mutations can be inherited or acquired during a person's lifetime. Mutations that an individual inherits from their parents are called hereditary mutations. They are present in all body cells and can be passed down to new generations. Acquired mutations occur during an individual’s life. If an acquired mutation occurs in an egg or sperm cell, it can be passed down to the individual’s offspring. Once an acquired mutation is passed down, it is a hereditary mutation. Acquired mutations are not passed down if they occur in the somatic cells, meaning body cells other than sperm cells and egg cells. Some acquired mutations occur spontaneously and randomly in genes. Other mutations are caused by environmental factors, such as exposure to certain chemicals or radiation.
Mutations occur throughout the natural world. Some mutations are beneficial and increase the possibility that an organism will thrive and pass on its genes to the next generation. When mutations improve survival or reproduction, the process of natural selection will cause the mutation to become more common over time. When mutations are harmful, they become less common over time. Therefore, mutation is a force that helps drive evolution.
