Mutations
General Definition
Long Notes:
• Any change in DNA sequence is called a mutation.
Abbreviated Notes (AN):
• Mutation (mut) = DNA sequence (seq) change
General Definition
Long Notes:
• Mutations may affect only one gene, or they may
affect whole chromosomes.
(AN):
• Mut – 1 gene or whole chromosome
Types
Long Notes:
• There are three basic types of mutations:
– Point Mutation
– Frameshift Mutation
– Chromosomal Mutation
(AN):
• 3 types mut.:
– Point Mut. (PM)
– Frameshift Mut. (FM)
– Chromosomal Mut. (CM)
Point Mutations
Long Notes:
• A point mutation is a change in a single base pair in
DNA.
(AN):
• PM = change in 1 base pair in DNA
Point Mutations
Long Notes:
• A change in a single nitrogenous base can change
the entire structure of a protein because a change
in a single amino acid can affect the shape of the
protein.
(AN):
• PM = 1 amino acid (AA) change, can change protein
shape
The effects of point mutations
Normal
mRNA
Protein
Stop
Replace G with A
Point
mRNA
mutation
Protein
Stop
Frameshift
Long Notes:
• A mutation in which a single base is added or
deleted from DNA is called a frameshift mutation
because it shifts the reading of codons by one
base.
(AN):
• FM = +/- 1 base, causes shift in codons
Frameshift mutations
Deletion of U
Frameshift
mutation
mRNA
Protein
Frameshift
Long Notes:
• This mutation would cause nearly every amino acid
in the protein after the deletion to be changed.
(AN):
• FM – causes most AA in protein after +/- to be
wrong
Frameshift
Chromosomal Mutations
Long Notes:
• Few chromosomal mutations are passed on to the
next generation because the zygote usually dies.
(AN):
• CM – zygote usually dies
Chromosomal Mutations
Long Notes:
• In cases where the zygote lives and develops, the
mature organism is often sterile and thus incapable
of producing offspring.
(AN):
• CM – if lives, usually sterile
Chromosomal Mutations
Long Notes:
• When a part of a chromosome is left out, a deletion
occurs.
A B C D E
F G H
A B C E
Deletion
(AN):
• CM – part left out = deletion
F G H
Chromosomal Mutations
Long Notes:
• When part of a chromatid breaks off and attaches
to its sister chromatid, an insertion occurs.
• The result is a duplication of genes on the same
chromosome.
A B C D E
F G H
A B C B C D E
F G H
Insertion
(AN):
• CM – gets duplicate part from sister chromatid =
insertion
Chromosomal Mutations
Long Notes:
• When part of a chromosome breaks off and
reattaches backwards, an inversion occurs.
A B C D E F G H
A D C B E
Inversion
(AN):
• CM – part flipping around = inversion
FG H
Chromosomal Mutations
Long Notes:
• When part of one chromosome breaks off and is
added to a different chromosome, a translocation
occurs.
AB C D E F G H
WX Y Z
WX AB C DE F G H
Translocation
Y
Z
(AN):
• CM – part breaks off & sticks to another
chromosome = translocation
General Results
Long Notes:
• Mutations in eggs or sperm affect future
generations by producing offspring with new
characteristics.
(AN):
• Mut. egg/sperm = pass offspring
General Results
Long Notes:
• Mutations in body cells affect only the individual
and may result in cancer.
(AN):
• Mut. body cells = cancer (maybe)
Reproductive Cells
Long Notes:
• The mutation may produce a new
trait or it may result in a protein
that does not work correctly.
(AN):
• maybe new trait, maybe bad protein
Reproductive Cells
Long Notes:
• Sometimes, the mutation results in a protein that is
nonfunctional, and the embryo may not survive.
(AN):
• protein doesn’t work, embryo might die
Reproductive Cells
Reproductive Cells
Long Notes:
• In some rare cases a gene mutation may have
positive effects.
(AN):
• + effects rare
Somatic Cells
Long Notes:
• Damage to a gene may impair the function of the
cell.
• When that cell divides, the new cells also will have
the same mutation.
(AN):
• Cell might not work right.
• Divides – new cells have mut.
Somatic Cells
Normal
Cell
Mutation
Normal
Cell
Normal
Cell
Normal
Cell
Normal
Cell
Mutated
Cell
Normal
Cell
Normal
Cell
Normal
Cell
Mutated
Cell
Mutated
Cell
Mutated
Cell
Mutated
Cell
Mutated
Cell
Mutated
Cell
Somatic Cells
Long Notes:
• Some mutations of DNA in body cells affect genes
that control cell division.
• This can result in the
cells growing and
dividing rapidly,
producing cancer.
(AN):
• Mut. might affect genes for mitosis.
• Too much growth/division = cancer.
Causes
Long Notes:
• Mutations can be caused by errors in replication,
transcription, cell division, or by external agents.
(AN):
• Mut. from replication, transcription, cell div. or ex.
agents.
Causes
Long Notes:
• Some mutations seem to just happen, perhaps as a
mistake in base pairing during DNA replication.
• These mutations are said to be spontaneous.
(AN):
• Spontaneous mut. “just happen”.
Causes
Long Notes:
• Any agent that can cause a change in DNA is called
a mutagen.
• Mutagens include radiation, chemicals, and even
high temperatures.
(AN):
• Mutagen – causes mut., radiation, chems, high
temps
Causes
Long Notes:
• Forms of radiation, such as X rays, cosmic rays,
ultraviolet light, and nuclear radiation, are
dangerous mutagens because the energy they
contain can damage or break apart DNA.
(AN):
• Radiation = Xrays, cosmic rays, UV light, nuclear
rad. (all high energy)
Causes
Long Notes:
• The breaking and reforming of a double-stranded
DNA molecule can result in deletions.
(AN):
• Deletions from break/remake DNA
Causes
Long Notes:
• Chemical mutagens include dioxins, asbestos,
benzene, and formaldehyde, substances that are
commonly found in buildings and in the environment.
(AN):
• Chemicals = dioxins, asbestos, benzene,
formaldehyde; in buildings & environment
Causes
Long Notes:
• Chemical mutagens usually cause substitution
mutations.
(AN):
• Chems – usually substitution mut.
Repairing DNA
Long Notes:
• Repair mechanisms that fix
mutations in cells have
evolved.
• Enzymes proofread the DNA
and replace incorrect
nucleotides with correct
nucleotides.
(AN):
• Evolved repair to fix mut.
like enzymes to proofread/
fix DNA
Repairing DNA
Long Notes:
• These repair mechanisms work extremely well, but
they are not perfect.
• The greater the exposure to a mutagen such as UV
light, the more likely is the chance that a mistake
will not be corrected.
(AN):
• Good, not perfect.
• More mutagen, more chance of mistake.
Any change in DNA
sequences is called a
_______.
A. replication
B. mutation
C. transcription
D. translation
The answer is B.
Which is more serious, a
point mutation or a
frameshift mutation? Why?
A frameshift mutation is more
serious than a point mutation
because it disrupts more
codons than a point mutation.
Why are chromosomal
mutations rarely passed on
to the next generation?
Few chromosomal changes are
passed on to the next generation
because the zygote usually dies.
If the zygote survives, it is often
sterile and incapable of producing
offspring.