Biological Sciences
Gene Mutations
Gene mutations are changes in the DNA sequence that can result in altered or non-functional proteins. They can occur spontaneously or be induced by external factors such as radiation or chemicals. Mutations can have various effects, from causing genetic disorders to contributing to the diversity of species through evolution.
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7 Key excerpts on "Gene Mutations"
eBook - ePubThe Human Genome in Health and Disease
A Story of Four Letters
- Tore Samuelsson(Author)
- 2019(Publication Date)
- Garland Science(Publisher)
5 Variants in the Human Genome Sequence and Their Biological SignificanceT his chapter covers some more background as to the human genome, before we go on to discuss the role of the protein coding sequences in Chapter 6 .The genomes of humans and all other living organisms are not static over time but are subject to changes. We refer to such alterations of the nucleotide sequence as mutations or variants . Mutations are necessary for evolution to proceed, but sometimes they are harmful. One example of such a mutation is the A to T nucleotide substitution associated with sickle cell anemia. Throughout this book, we examine the effect of mutations in the human genome, because they give important clues as to the normal function of different sequence elements.In this chapter, we look into the consequences of mutations in the human genome. Human individuals are genetically different, and we need to understand the nature of these differences. Next, we see how the human genome sequence is related to disorders and traits. We also discuss cancer, one important category of serious diseases with a genetic background. But first we examine some general aspects of mutations and their molecular causes.Types of MutationsMutations involve one or a few nucleotides only or they may involve larger regions (say 1,000 nucleotides or more) of DNA sequence. The mechanisms by which these two categories of mutations arise are different. In this chapter, we focus on the smaller changes that may be classified into substitution mutations (or point mutations), where one nucleotide is replaced with another, and insertions /deletions , also known as indels where a small number of nucleotides (mean length about 10, median 6) are inserted or deleted as compared to the original sequence. Throughout this book a mutation is represented with an expression like “A > G,” meaning that an A has changed into G. The reader should be aware that a mutation often first appears on one of the DNA strands, but after replication of DNA the mutation is observed on both strands. For instance, for the “A >
eBook - PDF- Matthew B. Hamilton(Author)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
The following sections will present classical population genetic models for the fate of a new mutation, the impact of mutation on allele fre- quencies in a population, and the predicted balance between the removal of genetic variation by genetic drift and its replacement by mutation. This chapter will also cover several models of the way new alleles are introduced by mutation commonly employed in population genetics, illustrated with applications that highlight the consequences of these models. The final section of the chapter will show how the process of mutation can be incorporated into genea- logical branching models. Mutation is a broad term that encompasses a wide variety of events that lead to alterations in DNA sequences. Point mutations lead to the replace- ment of a single base pair by another nucleotide. Point mutations to chemically similar nucleotides (purine to purine (A G) or pyrimidine to pyrimidine (C T)) are called transitions, while point muta- tions to chemically dissimilar nucleotides (purine to pyrimidine or pyrimidine to purine) are called transversions. Base substitutions that occur within coding genes may or may not alter the protein pro- duced by that gene. Synonymous or silent muta- tions result in the same translation of a DNA sequence into a protein due to the redundant nature of the genetic code, while nonsynonymous or mis- sense mutations result in a codon that does change the resulting amino acid sequence. Mutation can take the form of insertion or dele- tion of DNA sequences, often referred to by the short-hand indels. Indels within coding regions result in frameshift mutations if the change in sequence length is not an even multiple of three, altering the translation of a DNA sequence and possibly creating premature stop codons. Indels may range in size from a single base pair to segments of chromosomes containing many thousands of base Population Genetics, Second Edition.
eBook - ePub- David P. Clark(Author)
- 2009(Publication Date)
- Academic Cell(Publisher)
An error in a cell’s genetic material is known as a mutation. As might be expected, many mutations are detrimental. However, detrimental mutations tend to be overestimated because they are more noticeable. Very often the negative effect is minimal, and in fact, the majority of mutations have little or no significant effect on the survival of an organism—they are essentially neutral. Furthermore, occasional mutations may turn out to be beneficial to the survival and reproduction of the organism. The accumulation of such beneficial mutations allows the organism to evolve in response to changing environmental conditions (see Ch. 20). Mutations are heritable alterations in the genetic material of any organism or gene creature. At the molecular level, mutations are alterations in the DNA molecules of which the genes are made. Consequently, when a DNA molecule replicates, any changes due to mutation of the original DNA base sequence will be duplicated and passed on to the next generation of cells. In single-celled organisms, mutations are passed on from one generation to the next when the organism divides. Among multi-cellular organisms, the situation is more complicated. Mutations are inherited by the next generation of organisms only if they occur in the cells of the germ line and are passed on during sexual reproduction. Mutations that occur in somatic cells will only be passed on to the descendents of those cells. Such mutant cell lines will be restricted to the original multi-cellular organism where the mutation occurred. Somatic mutations that result in unregulated cell growth are responsible for the emergence of cancers. Other somatic mutations merely result in particular cell-lines or organs being genetically different from the rest of the body. Since the DNA is used as a template in transcription to make an RNA copy, a mutation in the DNA sequence within a cell will be passed on to the mRNA molecule. Finally, the mRNA is translated to yield protein
eBook - PDF- Mark Ridley(Author)
- 2009(Publication Date)
- Wiley-Blackwell(Publisher)
These errors are called mutations. The new sequence of CHAPTER 2 / Molecular and Mendelian Genetics 27 .. Protein chain Transfer RNA Messenger RNA Ribosome Chromosome Gene Messenger RNA Translation Protein Figure 2.3 The transfer of information in a cell. Much of the DNA does not code for genes DNA that results from a mutation may code for a form of protein with different prop- erties from the original. Mutations can happen in any cell, but the most important mutations, for the theory of evolution, are those occuring in the production of the gametes. These mutations are passed on to the offspring, who may differ from their parents because of the mutation. Various kinds of mutation can occur. One is point mutation, in which a base in the DNA sequence changes to another base. The effect of a point mutation depends on the kind of base change (Figure 2.4a– c). Synonymous, or silent, mutations (Figure 2.4a) are mutations between two triplets that code for the same amino acid, and have no effect on the protein sequence. Non-synonymous, or meaningful, point mutations do change the amino acid. Because of the structure of the genetic code (Table 2.1), most synonymous mutations are in the third base position of the codon. About 70% of changes in the third position are synonymous, whereas all changes in the second and most (96%) at the first position are meaningful. Another distinction for point muta- tions is between transitions and transversions. Transitions are changes from one 28 PART 1 / Introduction .. Original DNA sequence …C C G C T C G T C A A C T A G… …Gly . Glu . Gin . Leu . Ile… …C C G C T T G T C A A C T A G… …Gly . Glu . Gin . Leu . Ile… C → T …Gly . Glu . Gin . Ser . Ile… A → G …C C G C T C G T A G C T A G… A → C …C C G C T C G T C C A C T A G… …Gly . Glu . Gin . Val . Ile… Insert C …C C G C C T C G T C A A C T A G… …Gly .
- Yuri Kartavtsev(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
6 GENES, MUTATIONS AND EVOLUTION MAIN GOALS 6.1 Introduction to the Study of Mutation 6.2 Structure and Functions of Genes 6.3 Types of Mutations on DNA Level 6.4 Mutations and Amino Acid Substitutions 6.5 Mutation Rate 6.6 TRAINING COURSE, #6 SUMMARY 1. Mutations lead to the alteration of a current phenotype or to creation of variability, and by this provide a subject for genetic research. Due to this, their importance for genetics and evolution of life in general is obvious. 2. In terms of their function, genes can be classi fi ed into two groups: protein-coding or structural genes and RNA-coding or regulatory genes . Structural genes may participate in regulation too, and in this have no principal difference from the second group of genes. 3. Nucleotide substitutions can be divided into two different classes: transition and transvertion . Transition is the substitution of a purine for another purine (A G) or the substitution of a pyrimidine for another pyrimidine (T C). Transvertions are inverse types of nucleotide substitutions, when a purine is substituted by a pyrimidine and vice versa (G T, A C, C G or A T). 4. Classical geneticists have determined that the rate of mutations, that alter phenotypic characters or induce lethal effects, is of the order of 10 –5 per locus per generation in eukaryotes such as man, Drosophila and corn. The mean rate of amino acid substitution for an average polypeptide is estimated to be 70 Molecular Evolution and Population Genetics for Marine Biologists 4 × 10 –7 per locus per year. Due to the evidences that electrophoresis detects only about one-quarter of all amino acid changes, the rate of amino acid substitutions detectable by electrophoresis is estimated to be about 10 –7 per locus per year. 5. Mutations play the principal role in molecular clocks .
eBook - PDF- Dietrich Stauffer(Author)
- 2000(Publication Date)
- World Scientific(Publisher)
This way, models of molecular evolution may appear next to those used in animal breeding. This should not be misunderstood as neglect of the historical context or the biological motivation; however, it is felt that the classical and molecular fields should (and do!) intermingle, and much can be gained by considering their mutual relationships. 4.1. Mutation models If the genotype is a collection of sites, it is usually assumed that all sites mutate independently and experience the same transition probabilities. With binary variables at the sites, mutation is either chosen symmetric or unidirectional. Biological Evolution Through Mutation, Selection, and ... 221 Symmetric mutation is more adequate for the molecular context, whereas uni-directional mutation is often used in the classical regime. The notion behind the latter is that, actually, multiple alleles per site are assumed, but they are lumped into a (small) wild type and a (large) mutant class, where muta-tions from wild type to mutant are predominant and back mutations negligible, due to sheer entropic reasons. With a £ {+, — } L and symmetric mutation with probability p per site at every reproduction event, the mutation probability from
eBook - PDFHuman Heredity
Principles and Issues
- Michael Cummings(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
From Yashon/Cummings, Human Genetics and Society, 2E. © 2012 Cengage Learning Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 11-4 Mutations Can Be Spontaneous or Induced | 243 Chemical changes in bases can cause mutations. The purine and pyrimidine bases in nucleotides can exist in alternate chemical forms that depend on small atomic changes within the molecule called tautomeric shifts . These shifts change the hydrogen bonding properties of bases and allow bonding with noncomplementary bases ( Figure 11.5 ) that can lead to permanent base changes in sequence following replication. Keep in mind that many DNA mutations that begin as tautomeric shifts can also be induced by external agents. Radiation is a source of mutations. In addition to spontaneous mutations, such as those generated by errors in DNA rep-lication, several environmental agents, including radiation, can damage DNA. Simply defined, radiation is a process by which energy travels through space. For example, the heat from a fire in a fireplace travels through space and warms a room. Exposure to radiation is unavoidable. Everything in the physical world contains sources of radiation. This includes our bodies, the air we breathe, the food we eat, and the bricks in our houses. These natural sources of radiation are called background radiation . We are also exposed to radiation that results from human activity, including medical testing, nuclear testing, nuclear power, and consumer goods. Radiation can cause biological damage at several levels.
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