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MUTATIONS!
Part One
Scott Hatfield
Bullard Science Department
MUTATIONS, PART 1:
WHAT ARE THEY ?
MUTATIONS:

are changes in the genetic material of
the cell.
MUTATIONS:

are changes in the genetic material of
the cell.

can occur at the level of an individual
DNA strand (a point mutation) or to an
entire chromosome (a chromosomal
mutation)
MUTATIONS:

usually lead to a decrease, rather than
an increase, of information.

A loss of information in the cell leads to
a loss of some function.
Information is lost….
Information is lost….
Information is lost….
Information is lost….
The loss of information means
that most mutations are either
harmful or have no effect.
The loss of information means
that most mutations are either
harmful or have no effect.
The loss of information means
that most mutations are either
harmful or have no effect.
The loss of information means
that most mutations are either
harmful or have no effect.
.
Now and then a mutation will
offer a benefit to an organism.
.
However, the idea that a single mutation would lead
to a huge, dramatic change in a single generation
(like the X-Men characters) is just wrong.
TYPES OF MUTATIONS:

Point mutations are caused by random
errors in the copying process (during
transcription)
TYPES OF MUTATIONS:

Chromosomal mutations occur when
chromosomes fail to properly separate
during meiosis
Chromosomal
Mutations:
chromosome
nucleosome
DNA
double
helix
coils
supercoils
histones
Chromosomal
Mutations:
• changes in the number
or structure of chromosomes
Chromosomal
Mutations:
• changes in the number
or structure of chromosomes
• typically harmful in humans
Chromosomal
Mutations:
• can occur in four different ways:
deletion, duplication, inversion
and translocation
Chromosomal
Mutations:
DELETION
Chromosomal
Mutations:
DELETION
DUPLICATION
Chromosomal
Mutations:
DELETION
DUPLICATION
INVERSION
Chromosomal
Mutations:
DELETION
DUPLICATION
INVERSION
TRANSLOCATION
Non-Disjunction:
• is the failure of the chromosomes
to properly separate during
meiosis
Meiosis II:
Meiosis I: non-disjunction
homologous chromosomes
fail to separate
Non-Disjunction:
• leads to organisms with the
wrong number of chromosomes
• causes birth defects like Down’s
Syndrome (trisomy-21)
POINT
Mutations:
chromosome
nucleosome
DNA
double
helix
coils
supercoils
histones
POINT
Mutations:
• are changes in single base pairs of DNA
•
can lead to production of faulty
(misshapen) proteins, or no
protein at all
POINT
Mutations:
• often have no
effect: UCC
codes for
serine, for
example, but so
does UCU, UCA
or UCG
• that change the last letter in a DNA
triplet may lead to the same amino acid
POINT
Mutations:
• that do this are called sense or
silent mutations
POINT
Mutations:
• which lead to
a different
amino acid,
however, are
called missense
mutations
• Depending on the amino acid,
these can be good, bad or neutral
POINT
Mutations:
• which lead to
a stop codon
(UAA, UAG or
UGA) are called
nonsense
mutations
•
These lead to loss of function
and are usually bad
POINT
Mutations:
• Sense, missense and nonsense
mutations are typically caused
by substitution of one nucleotide
for another, changing the
meaning of only one codon.
•
Deletion or insertion of an entire
nucleotide leads to frameshift !
Frameshift Mutations
alter everything that follows:
THE DOG ATE THE RAT MAN
THE HOG ATE THE RAT MAN
THE DOG ATE HER ATM AN…
THE OGA TEH ERA TMA N…
MUTATIONS!
Part Two
Scott Hatfield
Bullard Science Department
MUTATIONS, PART 2:
Where Do They Happen ?
?
?
?
?
MUTATIONS:

can occur in any cell

that occur in gametes (eggs or sperm)
are called germ-line mutations since
they occur during the germination of
new offspring (reproduction).

that occur in cells other than gametes
are called somatic mutations
Somatic Mutations:
Many are harmless: freckles, for example,
are often the result of such mutations.
(Three flies are shown above. Two are mutants.
Would these be harmless mutations, or not?)
Somatic Mutations:
Some are dangerous, because the
loss of information leads to the loss
of some critical function.
This fruit fly was born without functional eyes,
but it has a white ‘eye spot’ clearly visible on
its abdomen. Flying blindly is not a favored trait !
Somatic Mutations:
Some are dangerous, because the
loss of information leads to the loss
of some critical function.
This fruit fly was born without functional eyes,
but it has a white ‘eye spot’ clearly visible on
its abdomen. Flying blindly is not a favored trait !
Somatic Mutations:
Some are dangerous, because the
loss of information leads to the loss
of some critical function.
Somatic Mutations:
Some are very
dangerous,
because their loss
triggers runaway
cell division, also
known as . . .
Cancer!
How does this happen?
This is a picture of skin
cancer on a person’s
cheek, a somatic
mutation, probably
triggered by UV
radiation
Substances which tend to
cause mutations are
called mutagens. . .
High frequencies of ultraviolet light, for example,
can cause point mutations which lead to skin
cancer. Let’s see how this can happen . . .
Ultraviolet Light and
Mutation
Sunlight contains many
frequencies of radiation, but
most are filtered out by the
atmosphere.
Ultraviolet Light and
Mutation
Sunlight contains many
frequencies of radiation, but
most are filtered out by the
atmosphere.
UV-B radiation does get
through, however, triggering
a chemical change in DNA,
a point mutation
Ultraviolet Light and
Mutation
Sunlight contains many
frequencies of radiation, but
most are filtered out by the
atmosphere.
UV-B radiation does get
through, however, triggering
a chemical change in DNA,
a point mutation
(This can affect the health
of organisms like the plants
shown in the graphic)
Ultraviolet Light and
Mutation
UV-B radiation provides
energy that drives two
thymine nucleotides
together.
Ultraviolet Light and
Mutation
UV-B radiation provides
energy that drives two
thymine nucleotides
together.
These thymine dimers
pull in, effectively
eliminating a single
nucleotide.
Ultraviolet Light and
Mutation
UV-B radiation provides
energy that drives two
thymine nucleotides
together.
These thymine dimers
pull in, effectively
eliminating a single
nucleotide.
This single point mutation
also destroys information,
leading to loss of function.
Ultraviolet Light and
Mutation
Loss of function may
disrupt the regular cell
cycle (G1, S1, G2, mitosis
and cytokinesis)
Ultraviolet Light and
Mutation
Loss of function may
disrupt the regular cell
cycle (G1, S1, G2, mitosis
and cytokinesis)
If this happens, the cell
may divide more often
than it should !
Ultraviolet Light and
Mutation
Loss of function may
disrupt the regular cell
cycle (G1, S1, G2, mitosis
and cytokinesis)
If this happens, the cell
may divide more often
than it should !
Uncontrolled cell growth
goes by many names, but
the generic term is cancer.
When these mutations lead to
cancer, they are classified as
carcinogens.
When mutations lead to
cancer, they are classified as
carcinogens.
Tobacco products contain
many ingredients known
to cause cancer and other
forms of lung disease.
Don’t let mutation
freak you out !
Don’t let mutation
freak you out !
Don’t let mutation
Freak you out !
Don’t let mutation
Freak you out !
It’s normal for humans
to have a certain number
of somatic mutations
during their life.
It’s normal for humans
to have a certain number
of somatic mutations
during their life.
It’s also healthy for all of us
to avoid mutagens
whenever possible!
We should avoid mutagens
because most mutations are
highly unlikely to offer benefits,
but (interestingly enough)
scientists have found the study
of mutations very helpful!
ALLELES:
• are different versions of the
same gene
• come in pairs (one from each
parent)
ALLELES:
• can be either dominant
(always expressed) or
recessive (hidden, and only
expressed when there are
no dominant alleles present)
ALLELES:
• whatever you have, whether
dominant or recessive, make up
the organism’s genotype
• the traits that are actually
shown are the phenotype
ALLELES:
• different combinations lead to
different genotypes which may
still have the same phenotype
ALLELES:
• As an example, a fly with two
dominant alleles and a fly with
one dominant allele and one
recessive allele will both have
the same phenotype !
ALLELES:
• another complication is that
not all alleles are expressed all
the time, in every part of the
organism’s body. Their
expression may be hidden.
In figuring these things out, scientists
have found mutations helpful, because
the errors in development reveal the
locus (actual physical location) of the
normal allele. So research on organisms
like fruit flies often involves deliberately
using mutagens to cause mutations that
reveal the normal allele and, eventually,
that allele’s function.