8.7
Mutations
The student is expected to:
6E identify and illustrate
changes in DNA and evaluate
the significance of
these changes
TEKS 6E
8.7
Mutations
TEKS 6E
KEY CONCEPT
Mutations are changes in DNA that may or may not
affect phenotype.
8.7
Mutations
TEKS 6E
Some mutations affect a single gene, while others affect
an entire chromosome.
• A mutation is a change in an organism’s DNA.
• Many kinds of mutations can occur, especially during
replication.
• A point mutation substitutes one nucleotide for another.
mutated
base
Substitutions: where one base
is changed to another. These
usually affect only one amino
acid.
MISSENSE: only
changes one amino acid
Original DNA:
The fat cat ate the rat.
Mutant DNA:
The fat hat ate the rat.
(substitution)
Substitution
: Changes a stop codon to appear too soon,
shortening the protein
SILENT: NO changes in
amino acid
8.7
Mutations
TEKS 6E
• Many kinds of mutations can occur, especially during
replication.
– A frameshift mutation inserts or deletes a nucleotide in
the DNA sequence.
–
These usually affect a large part of the protein. Remember, bases
are read in groups of three, but if one base is added or removed,
this shifts the “reading frame” of the genetic code and can change
all amino acids after the site of the mutation
Original DNA:
The fat cat ate the rat.
Insertion
Mutant DNA:
The fat cat tat eth era t.
(insertion)
Deletion
TAG CAT GGA AT
AUC GUA CCU UT
Ile
Val
Pro
8.7
Mutations
TEKS 6E
• Chromosomal mutations affect many genes.
• Chromosomal mutations may occur during crossing over
– Chromosomal mutations affect many genes.
– Gene duplication results from unequal crossing over.
8.7
Mutations
TEKS 6E
• Translocation results from the exchange of DNA segments
between nonhomologous chromosomes.
2. Chromosomal mutations: involve changes in the
number or structure of the chromosomes.
c.
Can change the locations
of genes on
chromosomes
i. Inversion: reverses
the direction of parts
of the chromosomes
ii.
Translocation: part of
one chromosome
breaks off and
attaches to another.
Original
Chromosome
Inversion
Translocation
d.
Can change the
number of copies of
some genes
i.
Deletion: a part of the
chromosome is lost
ii.
Duplication: there is
an extra copy
of part of the
chromosome
Original
Chromosome
Deletion
Duplication
8.7
Mutations
TEKS 6E
Mutations may or may not affect phenotype.
• Chromosomal mutations tend to have a big effect.
• Some gene mutations change phenotype.
– A mutation may cause a premature stop codon.
– A mutation may change protein shape or the active site.
– A mutation may change gene regulation.
blockage
no blockage
8.7
Mutations
TEKS 6E
• Some gene mutations do not affect phenotype.
– A mutation may be silent.
– A mutation may occur in a noncoding region.
– A mutation may not affect protein folding or the active
site.
8.7
Mutations
• Mutations in body cells do not affect offspring.
• Mutations in sex cells can be harmful or beneficial to
offspring.
• Natural selection often removes mutant alleles from a
population when they are less adaptive.
TEKS 6E
8.7
Mutations
Mutations can be caused by several factors.
• Replication errors can cause
mutations.
• Mutagens, such as UV ray and
chemicals, can cause mutations.
• Some cancer drugs use
mutagenic properties to kill
cancer cells.
TEKS 6E