Biology 100/101
Lecture 15: Mutations
Text readings in Life by Ricki Lewis:
Chapter 14, Chromosomes, pp. 301-304
Chapter 15, DNA Structure and Replication, pp. 319-322
Chapter 16, Gene Function, pp. 338-345
Review questions:
Pg. 347; questions 15 and 16
"To think about":
Pg. 347; questions 2, 5, 9, and 10
Answers to many of these questions can be found on the "Answers to End-of-Chapter Questions" page at the text website.
For feedback, post possible answers and ideas in the folder "Text 'Review' and 'To Think About' Questions" in the Biology Chat Section of Web Crossing.
Web resources: Mutations
Objectives:
After studying this material you should be able to:
- Define the term mutation and describe how mutations can occur.
- Describe how a mutation might occur, different types of mutations, and the
effect of the mutation, if any, on the protein that is produced when the gene
is expressed.
- Explain the causal relationship between mutation and inherited conditions involving protein abnormalities like cystic fibrosis, xeroderma pigmentosum and sickle cell disease.
- Distinguish between germinal and somatic mutations and describe the consequences of each for a person's children.
What are mutations?
A mutation is any physical change in the genetic material (such as a gene or a chromosome). A mutation is not necessarily bad (it may even be good).
Types of mutations
Causes of Mutation:
-
Spontaneous mutations
- DNA sequences are altered
- Induced Mutations
- exposure to chemical or environmental mutagens
Note: UV light is a carcinogen. (Fig. 15.14, p. 319 text) See suntan.
Genetic Mutations and the Effect on Protein
Genetic code (See Lewis text, p. 333).
- Point mutations - changes in single DNA nucleotides.
Part of gene
to be transcribed | CTG / TTA / CGC | Mutation 1 | CTG /TTG / CGC | Silent |
|
| Mutation 2 | CTG /TTT / CGC | Missense |
|
| Mutation 3 | ATT /TTA / CGC | Nonsense |
- What is the mRNA sequence without mutation? With mutation 1, 2, and 3?
- What is the amino acid sequence without mutation? With mutation 1, 2, and 3?
- Frameshift mutations: Additions or Deletions of one or more nucleotides.
Part of gene
to be transcribed | CTG / TTA / CGC | Mutation 1 | CTA / GTT / ACG / C | Addition |
|
| Mutation 2 | CT_T / TAC / GC | Deletion |
|
| Mutation 3 | CTG / CTG / TTA / CGC | Expansion |
- How many bases must be added or deleted to cause a frameshift?
- How many bases may be added or deleted WITHOUT causing a frameshift?
- How will additions, deletions, or expansions affect the amino acid make up of the protein?
- Some genes have repeated 3 base sequences, and the number of these may increase in 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).
Word Analogies for types of Mutations
Table 16.7 (text, p. 343) 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 |
Somatic Mutations versus Germinal Mutations
Somatic Mutations (Greek Soma= body)
Mutations in the body cells of an organism, any cell type EXCEPT egg and sperm.
Effects??
Germinal Mutations (Greek germinare= to sprout)
Mutations in cells that produce gametes (eggs and sperm).
Effects??
Some Mutation Examples
Mutations: Not all bad
- Mutations may occur in non-coding regions of DNA.
- Non-expressed regions of DNA.
- Introns removed
- Silent mutations
- Mutations as the ultimate source of genetic variation
- Genetic variability is essential to the survival of a species and the process of evolution.
Take me away.