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9: Mutation and Variation

Last updated

Jan 21, 2020
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- 8.13: Critical Thinking Questions
- 9.1: Mutation and Polymorphism

Ying Liu
City College of San Francisco

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The techniques of genetic analysis discussed in the previous chapters depend on the availability of two or more alleles for a gene of interest. Where do these alleles come from? The short answer is mutation. Humans have an interesting relationship with mutation. From our perspective, mutations can be extraordinarily useful, since mutations are need for evolution to occur.Mutation is also essential for the domestication and improvement of almost all of our food. On the other hand, mutations are the cause of many cancers and other diseases, and can be devastating to individuals. Yet, the vast majority of mutations probably go undetected.In this section, we will examine some of the causes and effects of mutations.

9.1: Mutation and Polymorphism
This page discusses how DNA transmits genetic information reliably but can undergo mutations, affecting phenotype and leading to classification into mutants. It differentiates between mutations and polymorphisms, noting that polymorphisms are common variants (over 1%) that do not imply normality. While mutations may cause diseases, polymorphisms can account for traits like hair color. Molecular markers, a specific type of polymorphism, are important for genetic research.
9.2: Origins of Mutations
This page discusses mutations, which are changes in DNA due to deletions, insertions, or substitutions, and can occur spontaneously or through mutagens. It highlights biological mutations from replication errors and mobile genetic elements called transposable elements (TEs), which disrupt gene functions and are classified as Class I (retrotransposons) and Class II (transposons). TEs are important for genome evolution, affecting gene structure, function, and genetic diversity.
9.3: Genetic screening for mutations- Forward genetics
This page details a method for identifying genes crucial to biological processes via mutant screening. Researchers induce mutations in a population and identify mutants with disrupted phenotypes linked to specific pathways, like memory in Drosophila. The process involves treating a parental population with a mutagen, targeting germline mutations that can be homozygous in offspring.
9.4: Types of Mutations
This page explains the five types of mutant alleles resulting from mutations: amorph (complete loss of function), hypomorph (partial loss of function), hypermorph (gain of quantity), neomorph (gain of new function), and antimorph (dominant opposite function). It highlights the dominance and recessiveness of these alleles and their impact on genetic expression and phenotype, contributing to a deeper understanding of mutation effects.
9.5: Some mutations may not have detectable phenotypes
This page discusses silent mutations that do not impact phenotypes, often found in non-coding regions or due to genetic redundancy. It mentions how some mutations in essential genes can result in recessive lethal alleles, making them difficult to detect. The text also explains the naming convention of genes based on mutant phenotypes rather than their normal functions, using the example of the white gene in fruit flies to illustrate potential confusion.
9.6: Complementation tests and Allelism
This page explains complementation tests in genetic research to identify whether mutations affecting similar traits are allelic or non-allelic. It uses examples, such as flower color, to demonstrate that crossing homozygous mutant strains results in wild-type offspring for non-allelic mutations or retains the mutant phenotype for allelic mutations. It highlights that true-breeding, recessive mutations are essential for these tests.
9.7: Example of Human Mutations
This page discusses cystic fibrosis (CF), an autosomal recessive disorder caused by CFTR gene mutations, particularly the ΔF508 mutation, which affects chloride ion transport and leads to mucus buildup in the lungs and other organs. It is more common in individuals of European descent. Kalydeco is a treatment for certain CFTR mutations, offering improved outcomes for some patients, albeit at a high cost.
9.8: Linkage and Mapping
This page discusses Mendel's Second Law of Independent Assortment, noting that while traits typically segregate independently, genes close together on a chromosome can exhibit linkage, which influences inheritance and genetic mapping. It explains that recombination through crossovers contributes to genetic diversity in meiosis, highlighting the importance of understanding linkage and recombination in heredity and evolution.
9.E: Mutation and Variation (Exercises)
9.S: Mutation and Variation (Summary)
This page discusses the differences between mutations and polymorphisms in DNA, noting that mutations are rare and can occur spontaneously or due to mutagens, while polymorphisms coexist within populations. It highlights the impact of mutations on gene function, the importance of identifying linked genes through phenotype screening, and the role of transposable elements in evolution.

Contributors

Dr. Todd Nickle and Isabelle Barrette-Ng (Mount Royal University) The content on this page is licensed under CC SA 3.0 licensing guidelines.

Thumbnail: The difference in appearance between pigmented and white peacocks is due to mutation. (Flickr-ecstaticist-CCANS)

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