Download Section 8.7 Mutations

Central Dogma of Molecular Biology
Genetic information flows in one direction –
from DNA to RNA to proteins.
Bellringer
What do these words mean to you?
Write a short 2 word definition for each
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1. Mutation
2. Duplication
3. Deletion
4. Insertion
5. Translocation
6. Inversion
7. Substitution
KEY CONCEPT
Mutations are changes in DNA that can affect phenotype
What are Mutations? (video link)
Mutations are changes to DNA that may be
• Harmful
• Helpful
• Have no effect.
When Mutations Occur
1. Errors can occur during:
DNA Replication
Protein Synthesis
Meiosis
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Causes of Mutations
2. Mutagens –
Environmental factors that cause
changes in DNA
Examples:
- Radiation
- Chemicals in environment
The effect mutations have on an organism’s
physical characteristics depends on:
1. The number and type of genes involved
2. Type of cell the mutation occurs in –
somatic or sex
Mutations in Somatic Cells:
• Affect only the organism they occur in.
• Cannot be passed to offspring.
Mutations in Sex (Germ) cells:
• May be passed to offspring
Two Categories of Mutations:
1.Single Gene – affects one gene – usually
caused by an error in DNA replication
2. Chromosomal – affects chromosomes –
usually error in meiosis .
Usually more harmful since many genes
are affected.
Types of Chromosomal Mutations
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Translocation
Duplication
Nondisjunction
Deletion
Inversion
• TRANSLOCATION
(“transfer location”)
• Piece of one chromosome breaks off and moves to a
nonhomologous chromosomes.
• DUPLICATION.
• Two or more copies of the same gene on a chromosome
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• NONDISJUNCTION
• Homologous chromosomes don’t separate in
Anaphase I
• Sister chromatids don’t separate in
Anaphase II
• Deletion
• Section of chromosome containing one or
more genes is removed
• Inversion
• Section of a chromosome flips its position
Single Gene Mutations
• Usually occur in DNA replication
• Affect one gene and the protein made from it
Types of Gene Mutations
Frameshift The insertion or deletion of a number of bases
that is not a multiple of 3. Alters the reading
frame.
Deletion
One or more bases are deleted. This alters the
reading frame
Insertion
One or more bases added to sequence..
Point
A single base change in DNA sequence. One
base is substituted for another Types of point
mutations are: nonsense, missense, or silent.
Nonsense
A change in the DNA sequence that results in
the coding for a stop codon instead of an
amino acid. Full protein not made.
Missense
Change in DNA sequence that results in a
codon that requests the wrong amino acid.
This type of mutation can be harmful, others
harmless
Silent
A change in the DNA sequence that does not
change the protein sequence.
Example
Frameshift Mutation
• Caused by adding or removing 1-2 bases
• Changes the reading frame
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Type of Frameshift Mutation
.Deletion - one or more bases are deleted; shifts
the reading frame
Type of Frameshift Mutation
Insertion - one or more bases are added; shifts
the reading frame
Point Mutations
• One nucleotide is replaced by another.
mutated
base
Types of Point Mutations
Determined by their outcomes
Nonsense point mutation
• Change codes for a STOP codon
• Full protein not made
• “NO” STOP
Missense Point Mutation
* Codes for wrong amino acid
* May be harmful or beneficial – depends…
Silent point mutation
Does not result in a different amino acid or protein made.
DNA changes but its expression (phenotype) does not.
Results of mutations may be:
• Harmful – needed protein isn’t made
• Have NO EFFECT – are not harmful or helpful
• Beneficial are favored by natural selection –
rarely occurs
Mutations increase genetic variety
Natural selection favors mutations that provide
survival advantage.
Laron Syndrome
mutation that causes dwarfism also protects
against cancer and diabetes.
• ABC Evening News - Laron Syndrome
• Mutations in body cells do not affect
offspring.
• Only Mutations in sex cells affect offspring.
• Natural selection favors mutations that
provide an adaptation that has survival
advantage