Mutation:Any change or error in DNA

• 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.

• However, problems may arise for the individual.

Mutagen: any agent that causes a change in DNA

• Radiation such as ultraviolet light, X rays, or radioactivity

• Chemicals including asbestos, cyanide, formaldehyde, tobacco

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

Substitutions will only affect a single codonTheir effects may not be serious unless they affect an amino acid that is essential for the structure and function of the finished protein molecule (e.g. sickle cell anemia)

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Substitution mutation causing sickle cell anemia

B. Inversion: two bases switch position

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Inversion mutation

GGTCCTCTCACGCCA

↓

CCAGGAGAGUGCGGU

↓

Pro-Gly-Glu-Cys-Gly

Inversion mutations, also, only affect a small part of the gene

C. Deletion: one base is deleted

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Deletion mutation

GGTC/CCTCACGCCA

↓

CCAGGGAGUGCGGU

↓

Pro-Gly-Ser-Ala-

A frame shift mutation, because it shifts the reading of codons by one base

D. 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 frame shift mutation, because it shifts the reading of codons by one base

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. Insertion: part of a chromatid breaks off and attaches to its sister chromatid.

(this can also be called a duplication)

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