Download chromosome mutations.

Blueprint of Life
Topic 19: Mutations
Biology in Focus, HSC Course
DOT POINT(s)
 discuss evidence for the mutagenic nature of radiation
 explain how mutations in DNA may lead to the
generation of new alleles
 explain how an understanding of the source of variation
in organisms has provided support for Darwin’s theory
of evolution by natural selection
Introduction
A mutation is a change in the genetic material of a cell— a
change in the sequence of nucleotides of DNA. All mutations do
not arise in the same manner—some mutations arise
spontaneously whereas others are induced.
evolution.berkeley.edu
Introduction
Mutations differ in their effect—some mutations may produce no
phenotypic change, whereas others produce little phenotypic
effect or significant effect.
handmadebymother.blogspot.com
Introduction
Mutations that are heritable (can be passed on to future
generations) are the direct source of all new alleles.
christinaa14.wordpress.com
Types of Mutations
Mutation is a collective term for
change in the DNA. The different
types of mutation can be distinguished
according to three things:
1. the amount of genetic material
changed: while most mutations affect
only a single gene (gene mutations),
there are some mutations that move
whole blocks of genes to other parts
of a chromosome or to another
chromosome entirely. These are called
chromosome mutations.
pinterest.com
Types of Mutations
A chromosome mutation is an unpredictable change that occurs in
a chromosome. These changes are most often brought on by
problems that occur during meiosis (cell division process of
gametes) or by mutagens (chemicals, radiation, etc.).
ahsmediacenter.pbworks.com
Types of Mutations
2. the effect of mutation on phenotype: mutations that do change
the phenotype of an individual may be harmful, beneficial or
neutral in their effect on the individual and its survival. The
phenotypic difference that a mutation produces may be present in
the individual only (somatic), or may be transmitted to future
generations (gametic).
www.mun.ca
Types of Mutations
Changes in DNA sequences
that may occur in somatic body
cells are called somatic
mutations and can only be
passed on to daughter cells
within an individual, when the
cells carrying the mutation
divide by mitosis, e.g.
mutations leading to skin
cancer in a person.
www.rollitup.org
Types of Mutations
Gametic mutations are those
where the mutation occurs
in the sexual reproductive
cells which give rise to
gametes (germ-line cells)
and these mutations are
heritable— that is, they can
be transmitted to future
generations, e.g. diseases
such as cystic fibrosis (gene
mutation) or Down
Syndrome (chromosome
mutation).
pinterest.com
Types of Mutations
3. the origin of the mutation: spontaneous mutations arise
randomly as a result of an error in a natural process such as DNA
replication in cells, whereas induced mutations arise as a result of
an environmental agent such as a chemical or radiation that
increases the chances of changes to nucleotide sequences.
www.livinginstrata.com.au
Mutagens
Environmental agents that cause mutations are termed
mutagens and research has shown that exposure to these
substances over a long period of time increases their harmful
effects (more so than simply giving a larger dose).
www.menshealth.co.uk
Mutagens
The process of inducing a mutation is
termed mutagenesis. There are many
mutagens known, including:
■ chemical mutagens:
— ingested chemicals: alcohol; tar in
tobacco smoke; chemicals in diet—
especially charred and fatty foods and
food additives and
preservatives (e.g. nitrites)
— irritants and poisons: organic
solvents such as benzene, cleaning
products; asbestos, coal tars; pesticides;
hair dyes, certain medications
www.hackforums.net
Mutagens
■ biological mutagens: some
viruses and micro-organisms
(e.g. hepatitis B virus, HIV,
Epstein-Barr virus) directly
influence the genetic material in
cells, changing the functioning
of genes and triggering cancers
www.llnl.gov
Mutagens
■ mutagenic radiation:
— ionising radiation: radioactive
materials from nuclear reactions
such as radiation from atomic
bombs, toxic spills (e.g. that at
Chernobyl), radiation used in
medicine (e.g. X-rays, gamma
radiation)
— ultraviolet (UV) radiation:
sunlight (and also the UV lights in
tanning salons).
www.greenbizletter.com
Mutagens
Today there are strict regulations on the amounts of mutagens
that may be present in products or to which people may be
exposed. Some chemicals are totally banned and others may be
added in very small amounts. Radiation doses are also regulated.
www.two-views.com
Mutagens
The old fashioned idea of consuming things ‘in moderation, not in
excess’ may have its merits, since it is the frequency and length of
exposure, rather than the amount in each dose, that is harmful.
blindgossip.com
The Mutagenic Nature of Radiation
During the late 1800s and early
1900s, many scientists were
involved in studying radiation.
Since the harmful effects of
radiation were unknown then,
scientists, such as Marie Curie,
who were exposed to large
amounts of radiation over
prolonged periods of time
developed various illnesses.
mariecurietpe.unblog.fr
The Mutagenic Nature of Radiation
Marie Curie worked with
ionising radiation for most of
her career and died from
leukaemia due to overexposure
to radioactive emissions. Many
years later survivors of the
1945 bombing of Hiroshima
suffered physical mutations as a
result of radioactive output
from the nuclear explosion.
www.biography.com
The Mutagenic Nature of Radiation
More recently, victims of the
nuclear meltdown in Chernobyl
in 1986 have suffered high
levels of infertility and genetic
mutations, as well as noncancerous side effects such as
cardiovascular and respiratory
conditions. Do you think there
will be any future problems
from the recent Japan nuclear
meltdown in 2011?
pinterest.com
Mutations May Lead to New Alleles
Mutations alter genes by changing the nucleotide sequence in
DNA. As a result one or more genes may be affected. If a gene is
altered from its original form the two variations of the gene are
termed alleles of that gene.
biology.about.com
Mutations May Lead to New Alleles
These changes to the genes may result in the production of new
proteins. Most new proteins have little effect on the organism,
but a few will lead to genetic disorders and inherited diseases
(e.g. a changed allele for the haemoglobin gene, results in the
disease sickle cell anaemia).
evolution.berkeley.edu
Mutations May Lead to New Alleles
Changes to genetic material in somatic cells are not passed on to
offspring— the new allele may cause a defect in an individual,
but will not affect future generations. However, mutations in
germ-line cells (gametic mutations) produce alleles that can be
inherited and may therefore have significant effects on
populations and so are important in evolution.
www.biologyreference.com
Gene Mutations
On a molecular level, mutations may
involve:
■ base substitution (point mutation):
one pair of nucleotides (e.g. A-T) is
substituted for another pair (e.g. GC).
■ frame shift (macromutation):
extra bases are added to or deleted
from a strand of DNA, changing the
whole sequence of nucleotides
■ a sequence within a gene may be
duplicated or translocated (moved).
rosalind.info
Chromosomal mutations
On a molecular level, if whole
chromosomes become rearranged
(deleted, duplicated or
translocated and attached to
another), a change in chromosome
number may arise. This usually
occurs as a result of chromosomes
not separating out correctly
during meiosis (that is, nondisjunction). The resulting cells
may have one chromosome less
than normal or one extra
chromosome.
www2.pearsonsuccessnet.com
Chromosomal mutations
The effect of a chromosomal mutation could result in disorders
such as Down syndrome, where individuals have three copies of
chromosome 21. This has numerous phenotypic effects (e.g.
slanting eyes; flat back of the head; short, broad hands; widely
spaced toes; growth failure; and mental retardation).
noahsdad.com
Chromosomal mutations
Most gene mutations produce recessive alleles because they
prevent the gene from producing a functional protein. Because of
this, we could all be carrying large numbers of mutations in our
genome and be completely unaware of them.
smithlabsafety.wikispaces.com
Chromosomal mutations
If the changed recessive alleles occur in the homozygous form in
individuals (or a dominant allele is present in even one copy) the
mutation can affect the phenotype of the individual. This
phenotypic change may be of advantage to the organism (e.g.
pesticide resistance in an insect), or it may be harmful (e.g. it may
cause a disease such as haemophilia).
pinterest.com
Chromosomal mutations
Some phenotypic changes that do not affect the individual
adversely (or in a positive way) may accumulate. They may become
beneficial or harmful to the organism and affect the overall
survival of a population if selective pressure arises as a result of
sudden environmental change (e.g. colouration in the peppered moth).
www.wired.com
Darwin Revisited
Mutation is the basic source of all
variation. Understanding
mutagenesis allows us to explain
how variations arise. The
understanding that mutations affect
the base sequence of DNA allows us
to understand how they can be
passed from one generation to the
next. It supports Darwin’s theory of
evolution because it provides a
mechanism to explain how heritable
variation arises.
skepticalteacher.wordpress.com
Darwin Revisited
A mutation will result in a change in phenotype that may be
negligible in its effect, or it may confer some advantage or
disadvantage to the organism. Mutations therefore provide the
diversity of genetic material that results in variation in
phenotype.
blog.arkive.org
Darwin Revisited
If mutations can be inherited, they provide the variation on which
natural selection acts, for evolution to occur. For evolutionary
purposes, a mutation can be redefined as a heritable change in the
genetic material.
www.rpdp.net
Activity/Homework
-Students to read Darwin Revisited article
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