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8.7 Mutations
KEY CONCEPT
Mutations are changes in DNA that may or may not
affect phenotype.
8.7 Mutations
Some mutations affect a single gene, while others affect
an entire chromosome.
A. A mutation is a change in an organism’s DNA.
B. 2 types of gene mutations. Also called Point
Mutations
1. A point mutation substitutes one nucleotide for
another.
2. A frameshift mutation inserts or deletes a
nucleotide in the DNA sequence.
mutated
base
8.7 Mutations
THE FAT CAT ATE THE RAT
1. Point Mutation: (substitution mutation)
THE FAT CTT ATE THE RAT
2. Frameshift Mutation: (insertion or deletion)
b. Add one nucleotide in (insertion)
THE FFA TCT TAT ETH ERA T (added in an “F”)
b. Take one nucleotide out (deletion)
THE ATC TTA TET HER AT (take out the “F”)
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How often do mutations occur?
“Extra”
Mutations occurs at a frequency of about 1 in every 1 billion
base pairs.
It is said that everybody has about 6 mutations in each cell
in their body!
8.7 Mutations
If I have that many mutations, then why don’t I look
weird?
“Extra”
Mutations are not always seen. The affected gene may still
function.
Silent Mutations
Mutations may be harmful.
Mutations may be beneficial.
Mutations may have no effect on the organism (Silent
Mutations)
8.7 Mutations
Gene Mutations “Fill into notes”
C. Some gene mutations change phenotype(appearance).
1. A mutation may cause a premature stop codon.
2. A mutation may change protein shape or the active
site.
3. A mutation may change gene regulation
D. Some gene mutations do not affect phenotype.
1. A mutation may be silent.
2. A mutation may occur in a noncoding region.
3. A mutation may not affect protein folding or the active
site.
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D. Chromosomal mutations affect many genes.
2. 2 types of chromosomal mutations.
1. Gene duplication results from unequal crossing over
2. Translocation results from the exchange of DNA segments between
nonhomologous chromosomes.
3. Chromosomal mutations tend to have a bigger affect on the individual.
8.7 Mutations
Chromosomal Mutation Examples
8.7 Mutations
E. Mutations in body cells (a cell of the arm or leg – to name
a few) do not affect offspring.
F. Mutations in sex cells (sperm or egg) can be harmful or
beneficial to offspring.
G. Natural selection often removes mutant alleles from a
population when they are less adaptive.
8.7 Mutations
Mutations can be caused by several factors.
1. Replication errors can cause
mutations.
2. Mutagens, such as UV ray, X
rays, and chemicals, can cause
mutations.
3. Some cancer drugs (radiation)
use mutagenic properties to kill
cancer cells.