Jayne has taught health/nutrition and education at the college level and has a master's degree in education.
What Are Mutations?
Have you ever wondered why you have brown hair and blue eyes, and your sibling has blond hair and brown eyes? It has to do with DNA - our genetic code that comes from our parents. Sometimes mistakes are made in the DNA when it is replicated or copied as each cell divides. When that happens, it can affect our appearance, how we behave, even whether we live or die.
An organism's DNA affects how it looks and behaves, and its physiology. A change in the DNA can cause changes in all aspects of its life. We often think of mutations as something negative, but that isn't always the case.
These errors, or changes in DNA, are essential to evolution. Without them, evolution could not occur. Usually, mutations are not good or bad, they're just different.
Mutations create slightly different versions of the same genetic information. The different versions are called alleles. They are what make each of us unique, by creating variation in hair color, skin color, height, shape, behavior, and our ability to fight off disease.
Variations that help an organism survive and reproduce are passed on to the next generation. Variations that hinder an organism's ability to survive and reproduce cause the organism to be eliminated from the population - in other words, the organism dies. This process, called natural selection, can lead to important changes in appearance, behavior, and/or physiology, in just a few generations. So, what are some of the types of mutations that occur?
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Types of Mutations
There are many types of DNA errors. The effects they may have on the individual vary from none at all to death. Mutations can be grouped into categories that are based on where the mutations occur.
- Somatic mutations, or acquired mutations, take place in non-reproductive cells. These are usually not passed on to the offspring. These can alter the division of cells, however. For example, the 'stop' codon may be altered, which would cause cells to divide out of control, resulting in cancer.
- Germ-line mutations occur in reproductive cells. These kind of mutations are passed on to the offspring. An example is albinism.
Mutations can also be categorized by the length of the nucleotide sequences they affect.
- Gene-level mutations are changes to short lengths of nucleotides. These affect physical characteristics and are important to large-scale evolution. An example would be insects becoming resistant to the insecticide DDT after repeatedly being exposed to it.
- Chromosomal mutations are changes to long lengths of nucleotides. These have serious consequences. An example is Down syndrome, where there are three copies of chromosome 21 instead of just two. This significantly affects the individual's appearance, cognition, and behavior.
What causes these types of mutations?
Causes of Mutations
Mutations occur from a variety of factors, including chance - this is called spontaneous mutation. Exposure to chemicals, ultraviolet radiation or other environmental factors, called mutagens, can also cause changes in DNA.
DNA is divided into codons, which are sets of three bases or nucleotides. The bases are adenine (A), cytosine (C), guanine (G), and thymine (T). The codons either specify an amino acid, which are building blocks for protein, or they signal the end of a protein.
The ways DNA can be changed include:
- Substitution, which is when one codon is switched with another. An example would be sickle cell anemia.
- Insertion, which is when extra base pairs are put into a new place in the DNA sequence.
- Deletion, which is when a section of DNA is lost or eliminated.
Let's sum up. Mutations are simply changes to DNA that create variation within a population. These variations make individuals within a population unique from each other by creating differences in hair color, skin color, height, shape, and behavior. The variations in DNA enable evolution to take place.
There are several types of mutations. Somatic mutations occur in non-reproductive cells, and are not passed on to offspring. Germ-line mutations occur in reproductive cells and are passed on to offspring. Gene-level mutations occur in short lengths of nucleotides, and chromosomal mutations affect long lengths of nucleotides.
Mutations are caused by many factors, including chance and mutagens. Some of the ways DNA can be changed include substitution, insertion, and deletion.
Once you are finished, you should be able to:
- Explain how DNA mutations lead to evolution
- List and describe the different types of genetic mutations
- Discuss some factors that can cause DNA mutations
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Mutations: When DNA Is Copied Wrong
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