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MUTATIONS
MUTATIONS
• The alteration of an organism’s
DNA
• Wide range of mutations
• Most mutations are
automatically repaired by the
organism’s enzymes…
• …therefore they have no effect.
MUTATIONS
• However…when the mutation
is NOT repaired…
• The resulting altered
chromosome/gene structure is
passed to ALL subsequent
daughter cells of the mutant
cell…
• Mutations can be good or bad.
When are mutations inherited?
• Mutations that occur in
regular body cells (somatic
cells) will affect all
daughter cells, but will not
be passed to offspring
• Can contribute to aging
process
• May lead to cancer…
When are mutations inherited?
For example:
• Mutation in lung cell will
lead to cancer, but cancer
isn’t passed on to
offspring
When are mutations inherited?
• Mutations will only be
passed on to offspring if
they occur in the gamete
(sex cells)
• Results in genetic
disorders
When are mutations inherited?
• Lethal mutations result in
the death of the organism
• Often miscarriage
What causes mutations?
• Malfunction during the process
of meiosis
• Exposure to a physical or
chemical agent
• Called a mutagen
• Examples: x-rays, chemicals
(asbestos, formaldahyde), UV
rays,
Two Types
1. GENE MUTATIONS—
• changes in a single gene (a
segment of DNA)
2. CHROMOSOMAL
MUTATIONS—
• changes in whole chromosomes
(chromosome number or
chromosome itself)
1. GENE MUTATIONS
a. POINT MUTATION (Substitution)
• Single nucleotide is substituted
for the wrong one
• Ex: A-G instead of A-T
• This can lead to…
1. GENE MUTATIONS
1) Silent mutation: has NO effect
since some amino acids have
multiple sequences
Ex: CUC codes for leucine
CUA also codes for leucine
1. GENE MUTATIONS
2) Missense mutation: causes the
wrong amino acid to be in
sequence
Ex: CUU codes for leucine
CCU codes for proline
1. GENE MUTATIONS
3) Nonsense mutation: causes an
early STOP codon
Ex: UCA codes for serine
UGA codes for STOP
POINT MUTATION—
SUBSTITUTION
THE FAT CAT ATE THE RAT
THE FAT CAT ATE THE HAT
1. GENE MUTATIONS
b. FRAMESHIFT MUTATION
• insertion or deletion of one or
more nucleotides
• All codons are shifted
• May cause serious effects
• Such mutations can alter a
protein so that it is unable to
perform its normal functions.
FRAMESHIFT MUTATION—
DELETION
THE FAT CAT ATE THE RAT
X FAT CAT ATE THE RAT
THE
TEF ATC ATA TET HER AT
FRAMESHIFT MUTATION—
INSERTION
THE FAT CAT ATE THE RAT
THE FAT CAT ATE THE RAT
THE FLA TCA TAT ETH ERA T
Disorders caused by
GENE MUTATIONS
•
•
•
•
•
Sickle-cell disease
Tay-Sachs disease
Huntington’s disease
Cystic Fibrosis
Albinism
2. CHROMOSOMAL MUTATIONS
a. DELETION
• Involves loss of a part
or whole chromosome
A
B
C
A
C
DELETION
D
E
F
D
E
F
2. CHROMOSOMAL MUTATIONS
b. DUPLICATION
• Opposite of deletion
• A segment of the
chromosome is repeated
A
B
B
C
A
B
C
DUPLICATION
D
E
F
D
E
F
2. CHROMOSOMAL MUTATIONS
c. INVERSION
• Direction of genes is
reversed within
chromosome (part is
upside-down)
A
B
C
A
E
D
INVERSION
D
E
F
C
B
F
2. CHROMOSOMAL MUTATIONS
d. TRANSLOCATION
• When part of a
chromosome breaks off
and relocates to another
part (non-homologous)
A
B
C
G
H
D
E
F
I
J
K
L
A
B
C
TRANSLOCATION
J
K
L
G
H
I
D
E
F
2. CHROMOSOMAL MUTATIONS
e. NONDISJUNCTION
• Results in too few or too
many chromosomes in a
cell…
NONDISJUNCTION
• MONOSOMY
• Having only ONE copy of a
chromosome instead of TWO
• EX: Turner’s syndrome (has
only one X chromosome)
NONDISJUNCTION
• TRISOMY
• Having THREE copies of a
chromosome instead of TWO
• EX: Down Syndrome (3
copies of chromosome #21,
trisomy 21)
NONDISJUNCTION
Disorders caused by
CHROMOSOMAL MUTATIONS
• NONDISJUNCTION of Sex
Chromosomes:
• Klinefelter’s syndrome (male)
• Turner’s syndrome (female)
• NONDISJUNCTION of
Autosomal Chromosomes:
• Down Syndrome (Trisomy 21)
Where can mutations occur?
Somatic Cells (Body Cells)
Germ Cells (Sex Cells)
Somatic Cells (Body Cells)
• During or before mitosis
• All new cells will also be
altered
• The change is permanent
• Only effects organism, not
offspring
Germ Cells (Sex Cells)
• Changes can occur in egg/sperm
before, during or after meiosis
• Altered egg/sperm may be
fertilized—passing change to
offspring
• Changes may or may not be
harmful
• Harmful changes cause birth
defects