Download Foundations of Biology

Mutations
Ch-Ch-Ch-Changes
Variation & Speciation
Variation also allows sexually reproducing
organisms to adapt to a changing environment.
The mechanism of mutation in DNA generates
variation with natural selection of individuals in
populations to produce new species.
How Mutation Works
Cell
DNA
Transcription
Translation
mRNA
Ribosome
Polypeptide
(protein)
©1998 Timothy G. Standish
Mutation
Mutation = Change
Biologists use the term “mutation” when
talking about any change in the genetic
material. Not all result in a change in
phenotype.
Macromutations
Four major types of Macromutations
are recognized:
1 Deletions - Loss of chromosome sections
2 Duplications - Duplication of
chromosome sections
3 Inversions - Flipping of parts of
chromosomes
4 Translocations - Movement of one part
of a chromosome to another part
Macromutation - Deletion
Chromosome
Centromere
Genes
A
B
C
D
E
F
A
B
C
D
G
H
G
H
E
F
Macromutation - Duplication
Chromosome
Centromere
Genes
A
B
C
D
E
F
G
H
A
B
C
D
E
F
EE
FF
Duplication
G
H
Macromutation - Inversion
Chromosome
Centromere
Genes
A
B
C
D
E
F
A
B
C
D
F
E
Inversion
G
H
G
H
Macromutation - Translocation
Chromosome
Centromere
A
B
C
A
B
E
Genes
D
F
E
C
F
G
H
D
G
H
Micro or Point Mutations
1
2
Additions - Addition of one or two
nucleotides
Deletions - Loss of one or two nucleotides
Micro Mutations
3’AGTTCAG-TAC-TGA-ACA-CCA-TCA-ACT-GATCATC5’
5’AGUC-AUG-ACU-UGU-GGU-AGU-UGA-CUAGAAA3’
Met
Thr
Cys
Gly
Ser
3’AGTTCAG-TAC-TGA-AAC-CAT-CAA-CTG-ATCATC5’
5’AGUC-AUG-ACU-UUG-GUA-GUU-GAC-UAG-AAA3’
Met
Thr
Leu
Val
Val
Val
Micro-mutations tend to have a dramatic effect on proteins as all
codons down stream from the mutation are changed and thus code
for different amino acids. As a result, the length of the polypeptide
may also be changed as a stop codon will probably come at a
different spot than the original stop codon.
Mutations Are Uncommon
Cells have many different mechanisms for
preventing mutations
These mechanisms make mutations very
uncommon
Even when point mutations occur in the DNA,
there may be no change in the protein coded for
Mutagens
• Mutations often occur naturally as a result of
random errors in replication.
• Environmental Factors
• Radiation
- X-ray
-Ultraviolet radiation
• Chemicals
- Mustard gas
- Chloroform
The Sickle Cell Anemia Mutation
Normal b-globin DNA
C
Mutant b-globin DNA
T
T
C
G A
A
G U A
mRNA
mRNA
Normal b-globin
Mutant b-globin
Glu
H2 N
C
C
A T
Val
O
OH
H
CH2
H2C
C OH
O Acid
H2 N
C
C
O
OH
H
CH
CH3
H3C
Neutral
Non-polar
Sickle Cell Anemia:
A Pleiotropic Trait
Mutation of base 2 in b globin codon 6 from A to T
causing a change in meaning from Glutamate to Valine
Mutant b globin is produced
Breakdown of
Red blood cells
Anemia
Clogging of small
Blood vessels
Tower skull
Weakness
Heart failure
Impaired
mental function
Accumulation of sickled
Cells in the spleen
Red blood cells sickle
Brain
damage
Paralysis
Pain and
Fever
Damage to
other organs
Rheumatism
Kidney
failure
Infections
Especially
Pneumonia
Spleen
damage