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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
Point mutatio
n
mRNA
Protein Stop
Stop
mRNA
Protein
Replace G with A
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
mRNA
ProteinFrameshif
t mutation
Deletion of U
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.
(AN):• CM – part left out = deletion
Deletion
A B C D E F G H A B C E 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.
(AN):• CM – gets duplicate part from sister chromatid
= insertion
Insertion
A B C D E F G H A B C B C D E F G H
Chromosomal Mutations
Long Notes:• When part of a chromosome breaks off and
reattaches backwards, an inversion occurs.
(AN):• CM – part flipping around = inversion
Inversion
A B C D E F G H A D C B E FG H
AB E FDCBX AWC HGGE HD F
WXY Z Y ZTranslocation
Chromosomal Mutations
Long Notes:• When part of one chromosome breaks off and is
added to a different chromosome, a translocation occurs.
(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
NormalCell
NormalCell
MutatedCell
Mutation
NormalCell
NormalCell
MutatedCell
MutatedCell
MutatedCell
MutatedCell
MutatedCell
MutatedCell
NormalCell
NormalCell
NormalCell
NormalCell
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 _______.
D. translation C. transcription B. mutation A. replication
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.
