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Chapter 12-4 DNA Mutations Notes
I. Mutations Introduction
A. Definition: Changes in the DNA sequence that affect genetic information
B. Mutagen= physical or chemical agent that interacts with DNA to cause mutations
1. Examples: UV radiation, chemicals
C. 2 categories of mutations
1. Gene Mutation (Point Mutation): mutation limited to one or two nucleotides in a single gene
2. Chromosomal Mutation: change in a portion of the whole chromosome.
a. Can affect more than one gene
II. Gene Mutations-
A. 3 Kinds of gene (Point) mutations-changes in one or a few nucleotides in a single gene
1. Substitutions-one base is replaced by another base
a. May not change the amino acid
i. Why?
Multiple codons specify the same amino acid (redundancy of the genetic code)
Example:
DNA: TAC GCA TGG AAT
mRNA: AUG CGU ACC UUA
A.A.: Met Arg Thr Leu
Mutation 1: TAC GCG TGG AAT
mRNA: AUG CGC ACC UUA
A.A: Met Arg Thr Leu
Same amino acid sequence-does not affect protein
function
DNA: TAC GCA TGG AAT
mRNA: AUG CGU ACC UUA
A.A.: Met Arg Thr Leu
Mutation 2: TAC TCA TGG AAT
mRNA: AUG AGU ACC UUA
A.A.: Met Ser Thr Leu
Different amino acid sequence-may or may not affect
protein function
2. Insertions-a base is added (inserted) into a gene
a. See Figure 12-20
Insertion
3. Deletions-a base is removed (deleted) from the gene
b. See Figure 12-20
4. Frameshift Mutations-shift in the readingframe of the genetic message.
1. Insertions and Deletions are examples of frameshift mutations
2. See Figure 12-20
a. ex: THE CAT ATE THE RAT
delete "C" THE ATA TET HER AT-
A mutation that affects every amino acid
following an insertion or deletion is called
a(an)
1. frameshift mutation.
2. point mutation.
3. chromosomal mutation.
4. inversion.
fram
eshift
muta
tion.
point m
utatio
n.
chro
moso
mal m
utatio
n.
inve
rsio
n.
0% 0%0%0%
20Answer Now
b. The order of amino acids changes depending on where you start reading.
c. If the 1st “G” is deleted the bottom sequence of amino acids will result & this is a completely different protein!! (Changes the “reading frame” of the genetic message)
The type of point mutation that usually
affects only a single amino acid is called
1. a deletion.
2. a frameshift mutation.
3. an insertion.
4. a substitution.
a dele
tion.
a fram
eshift
muta
tion.
an inse
rtion.
a subst
itutio
n.
0% 0%0%0%
20Answer Now
B. Summary: Types of Gene Mutations
1. Base pair substitution
2. Base pair insertion = Frameshift mutation
3. Base pair deletion = Frameshift mutation
III. Chromosomal Mutations-changes in the number or structure of chromosomes
A. Deletions, Duplications, Inversions, and Translocations
When two different chromosomes
exchange some of their material, the
mutation is called a(an)
1. inversion.
2. deletion.
3. substitution.
4. translocation.
inve
rsio
n.
deletio
n.
substi
tutio
n.
translo
catio
n.
0% 0%0%0%
20Answer Now
A mutation in which a segment of a
chromosome is repeated is called a(an)
1. deletion.
2. inversion.
3. duplication.
4. point mutation.
deletio
n.
inve
rsio
n.
duplicatio
n.
point m
utatio
n.
0% 0%0%0%
20Answer Now
A mutation in which all or part of a
chromosome is lost is called a(an)
1. duplication.
2. deletion.
3. inversion.
4. point mutation.
duplicatio
n.
deletio
n.
inve
rsio
n.
point m
utatio
n.
0% 0%0%0%
20Answer Now
1. May change the locations of genes on chromosome
2. May change the number of copies of some genes
IV. Significance of Mutations
A. Most mutations are neutral-they do not disrupt protein function
B. Some mutations can lead to cancer or disease
1. Changing just one amino acid-even if the protein is thousands of amino acids long –can cause the protein to change shape, not work properly, and sometimes cause diseases such as sickle cell, cystic fibrosis, and muscular dystrophy.
C. Some mutations can be passed on to offspring; only if the mutation is in the germline (sex cells)-we will discuss later in another chapter.
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