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