Mutation:Any change or error in DNA
What determines whether mutations are passed on to
offspring?
• If mutations occur in reproductive cells, the altered gene will become part of the genetic makeup of the offspring.
• If mutations occur in somatic cells (body cells), the mutation will not be passed on.
Mutagen: any agent that causes a change in DNA
• Radiation such as ultraviolet light, X rays, or gamma radiation
• Chemicals including asbestos, benzene, formaldehyde, nicotine
I. Point Mutation
• A change in a single base pair in DNA
mutatedbase
A. Substitution: one base is changed to another
Substitution mutation
GGTCACCTCACGCCA
↓
CCAGUGGAGUGCGGU
↓
Pro-Arg-Glu-Cys-Gly
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Substitution mutation causing sickle cell anemia
B. Insertion: one base is added
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Insertion mutation
GGTCTGCCTCACGCCA
↓
CCAGACGGAGUGCGGU
↓
Pro-Asp-Gly-Val-Arg
A frameshift mutation, because it shifts the reading of codons by one base
C. Deletion: one base is deleted
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Deletion mutation
GGTC CCTCACGCCA
↓
CCAG GGAGUGCGGU
↓
Pro-Gly-Ser-Ala-
Also a frameshift mutation
Question:
Which type of mutation would have a greater effect on the sequence of amino acids in a protein, a substitution mutation or a deletion mutation? Explain
II. Chromosomal Mutations• Occur during mitosis or meiosis; parts of
chromosomes break off and are lost or rejoin incorrectly.
• Pictures p. 321
A. Deletion: Part of a chromosome is left out
B. Duplication: part of a chromatid breaks off and attaches to its sister chromatid.
C. Inversion: part of a chromosome breaks off and is reinserted backwards
D. Translocation: part of one chromosome breaks off and is added to a different chromosome
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