Biology 100/101
Lecture 15
Mutations
(Print Version)

Announcements

Objectives

Web Resources

What are Mutations?

Types of Mutations

Effects on Proteins

Word Analogies

Lecture Activity

Causes of Mutations

Somatic/Germinal Mutations

Structure and Function

Not All Bad

Lecture Syllabus

IB 100/101 Home Page

Announcements

Text Readings in
Lewis et al.		 Testing Your Knowledge Thinking Scientifically
Chapter 13, Gene Function, pp. 255-260 Page 265, Questions 8-9 Page 266, Question 2

Answers to many of these questions can be found at the Text On-Line Learning Center

You may also ask questions and see answers to your classmates' questions in Web Crossing in the "Talk to Steve and Ed" discussion.

Also, try the Genetics Problems listed on pages 266-267! They're fun to do, and there are some possible examination questions here too! The answers are in the text.

Objectives:

After studying this material you should be able to:

  1. Define the term mutation.

  2. Describe the types of mutations that can occur in a gene and the effect, if any, they have on the protein that is produced when the gene is expressed.

  3. Describe how a mutation might occur by distinguishing between spontaneous and induced mutations.

  4. Distinguish between somatic and germinal mutations and describe the consequences of each for a person's child.

  5. Explain why mutations are not all harmful.

  6. Understand these terms:

    7. induced mutation spontaneous mutation germinal mutation
    somatic mutation missense mutation nonsense mutation
    frameshift mutation mutagen silent mutation

Web Resources:

What are Mutations?

  • A mutation is any physical change in the genetic material (such as a gene or a chromosome). When a gene contains a mutation, the protein encoded by that gene will be abnormal. Some protein changes are insignificant, others are disabling.

  • More than 4,000 diseases are thought to stem from mutated genes inherited from our parents.

  • A mutation may or may not affect the phenotype.

  • A mutation is not necessarily bad. It may even be good.

  • The ultimate of all mutations and The origin or these ultimate mutations, and some thought-provoking questions.

    • Types of Mutations

  • Chromosomal Mutations

  • Gene Mutations

    • Changes made by substituting a single base with another or by adding or deleting one or more nucleotides.

    Genetic Mutations and their Effects on Proteins

  • A Review of Protein Synthesis, by Access Excellence.

  • Gene Expression via Protein Synthesis, from Access Excellence. For a cell to make protein, the information from a gene is copied, base by base, from DNA into new strands of messenger RNA (mRNA). Then mRNA travels out of the nucleus into the cytoplasm, to cell organelles called ribosomes. There, mRNA directs the assembly of amino acids that fold into a completed protein molecule.

  • How are genes linked to disease? When a gene contains a mutation, the protein encoded by that gene will be abnormal.

  • There are many ways that mutations can occur and affect gene expression. To understand them, you need to refamiliarize yourself with the Genetic Code. The same Code is found in Table 13.2 in your text.

  • Point Mutations: Changes in single DNA nucleotides.

    • A missense mutation substitutes a different amino acid for the original one.

        • GAG (Glutamic Acid) --> GTG (Valine)
        ATG (Methionine) --> ATC (Isoleucine)

    • A nonsense mutation results in a stop codon being inserted someplace before the end of the gene.

        • GAG (Glutamic Acid) --> TAG (Stop Codon)

    • Silent mutations are point mutations that do not change the amino acid sequence of the protein. These are most likely to have no effect. Redundancy of the Genetic Code reduces the chance that point mutations do not alter the specified amino acids.

        • The codons GAA and GAG code for the amino acid Glutamic Acid (Glu).
        The codons GCU, GCC, GCA, and GCG all code for the amino acid Alanine (Ala).
        The codons GGU, GGC, GGA, and GGG all code for the amino acid Glycine (Gly).

    • Real examples of missense and nonsense mutations:
  • Frameshift Mutations: Additions or deletions of one or more nucleotides.

    • May result in "garbage" genes, as the entire amino acid sequence in the code after the change is devastated.

    • Large deletions may remove a single amino acid, or an entire chunk of chromosome. The most common mutation that causes severe cystic fibrosis deletes only a single codon.

    • Some genes have repeated base sequences, and the number of these may increase each generation. These expanding genes are responsible for increasingly severe cases of muscular dystrophy (CTG repeats), Huntington disease (CAG repeats), and Fragile X syndrome (CGG repeats).

        • Fragile X Syndrome:
        6-50 CGG repeats in an unaffected individual
        50-200 CGG repeats in a carrier
        >200 CGG repeats in an affected individual

    Word Analogies for Types of Mutations

  • Table 13.4 (text, p. 260) uses a sentence of three-letter words as an analogy to demonstrate the effects of mutations on gene sequence.

    • Wild type
    "Normal Gene"    		 THE ONE BIG FLY HAD ONE RED EYE
    Missense THQ ONE BIG FLY HAD ONE RED EYE
    Nonsense THE ONE BIG
    Frameshift THE ONE QBI GFL YHA DON ERE DEY
    Deletion THE ONE BIG HAD ONE RED EYE
    Duplication THE ONE BIG FLY FLY HAD ONE RED EYE
    Insertion THE ONE BIG WET FLY HAD ONE RED EYE
    Expanding (P) THE ONE BIG FLY HAD ONE RED EYE
    Expanding (F1) THE ONE BIG FLY FLY FLY HAD ONE RED EYE
    Expanding (F2) THE ONE BIG FLY FLY FLY FLY FLY FLY HAD ONE RED EYE

    Mutation Lecture Activity

    Causes of Mutations

  • Spontaneous mutations

  • Induced Mutations

    • Somatic Mutations vs. Germinal Mutations

    Somatic Mutations (Greek Soma= body)

    Germinal Mutations (Latin germinare= to sprout)

    Were these deformities the result of a somatic or germinal mutation?

    Relationship Between Protein Structure and its Function

    Mutations are Not All Bad