Transcript 4.2 Mutation - WordPress.com

Mutation
What is a Mutation?
A mutation is a change in the order of the A, G, T and C bases
in a gene. This causes the changed gene to make a different
protein which can alter the appearance or function of the cell
and/or the organism.
The White Kermode Bear or Spirit Bear
The White Kermode or Spirit bear is a black bear that had a
mutation (change in DNA bases) in just one nitrogen base in
one of its chromosomes when it was a fertilized egg. Just
one base changes in 1 out of 10 bears. The mutated gene will
not show it colour white unless a bear gets one mutated gene
from each parent (it needs two mutated genes to show the
white coat.).
The Inheritance of Spirit Bears
The gene for
white colour in
black bears is a
recessive gene.
As long as a
bear has 1
normal black
gene from 1 of
its parents, the
bear will be
black. It takes 2
white genes for
a bear to be
white. The black
gene shows its
trait over the
white gene.
The Spirit Bear Is
Being Protected
The Spirit Bear is
important in the
traditional culture of
the Tsimshian First
Nation. The B.C.
government has limited
the amount of logging
in the forests inhabited
by the bears.
Albino Mutants (Organisms With a Mutated Gene)
Many organisms have albino forms in which a single gene
has mutated or changed (because the DNA bases have
changed).
Different Kinds of Mutations
1.
A base (A,G,T,C) may be deleted.
…ACGTTACGA… may become …AGTTACGA…
2.
A base (A,G,T,C) may be added.
…ACGTTACGA… may become …ACGTGTACGA…
3.
A base (A,G,T,C) may be substituted.
…ACGTTACGA… may become …ACATTACGA…
Kinds of Mutations
1.
Positive Mutations are DNA changes that help an
organism to survive better.
2.
Negative Mutations are DNA changes that harm an
organism and make it less likely to survive. Most
mutations (90% + of all mutations) are this type.
3.
Neutral Mutations are DNA changes that have no harm or
benefit for an organism.
Positive Mutations
Some person who become infected with the HIV virus
(normally causing the disease, AIDS), have developed
mutations which prevent the HIV virus from infecting the
helper T cells.
Modern wheat developed from a grass which mutated and
doubled its number of chromosomes from 12 to 24.
Negative Mutations
Sickle Cell Anemia is one example of a negative mutation.
Sickle cells are red blood cells which have a slightly different
hemoglobin protein (HbS) from regular blood cells which
have normal hemoglobin.(Hb). In conditions of low oxygen,
sickle hemoglobin forms rods which stretch the red blood
cells into sickle-like shapes.
Sickle Cells – A
Negative Mutation
When sickle cells pass through
capillaries, they get stuck and
prevent blood flow which is lifethreatening. Symptoms for
persons with sickle cells
include pain, lethargy
(tiredness). Organs damaged
by lack of oxygen include
lungs, liver and kidneys.
A Single Nitrogen Base
Mutation in DNA
Sickle hemoglobin forms
when there is a single base
mutation in DNA. This
causes a new amino acid
to replace the normal
amino acid and this
change makes the sickle
hemoglobin function badly
(becoming rods) in low
oxygen conditions.
Inheritance of Sickle Cell Anemia (The Disease)
Sickle cell anemia is caused by a mutated gene on a
chromosome. Every person has two chromosomes of each
kind – one from their mother and one from their father. If a
person has one normal gene and one sickle gene, they are
called a carrier and rarely feel the severe effects of sickle cell
anemia. If a person has two sickle genes (one sickle gene
from each carrier parent) then a person has only sickle cells
and is very sick, likely to die at some point.
Sickle Cell Inheritance
If two parents are carriers of the sickle cell gene, the
probability is that 50% of their children will be carriers, 25%
normal and 25% having Sickle Cell Anemia.
Persons With African / Indian Ancestry More Likely
to Have Sickle Cell Genes
In Africa, having the Sickle gene was partly beneficial
because it protected persons from Malaria. Normal persons
were not protected from Malaria and thus died more, leaving
the Sickle gene to multiply in the African population.
Cystic Fibrosis is a disease
caused by a mutation in a
gene on a chromosome.
There are more than 1300
different mutations (different
changes in the DNA of this
gene) that have been
recorded. The normal gene
codes for a protein that
helps bring chloride ions
into and out of the cell.
When any of the 1300+
mutations occur, chloride
ions build up, causing a
thick mucous to form in
passages which blocks
passages in the lungs and
pancreas.
Negative Mutations
Cystic Fibrosis Symptoms and Treatment
A person with Cystic Fibrosis has difficulty breathing and
often gets lung infections. Pancreas secretions needed in
digestion get blocked by the mucous. Therapy includes
tapping and pommeling the chest and back to move the
mucous out of air passage ways. Special air vibrating
machines now accomplish this action.
Inheritance of Cystic Fibrosis
To get the disease, Cystic Fibosis, a person must receive a
mutated gene from both parents. If a person has one
mutated gene and a normal gene, the person will be normal
but will carry the gene and could pass it on to her/his
offspring.
Neutral Mutations
When a mutation has no positive benefits or negative affects,
it is called a neutral mutation. The White Spirit bear mutation
is considered neutral because it offers no advantage or
disadvantage for the bear that is white. For a different
organism, it could be an advantage (ex: an actic hare) or a
disadvantage (a white mouse in the woods).
Mutagens
Mutagens are substances or factors that can cause mutations
in DNA. Viruses, cigarette smoke, pollutants, Hg, asbestos,
certain chemicals and radiation all can cause mutations
(changes in the base code) in the DNA.
What Viruses Do in Organisms
A virus attaches
to a cell and
inserts its DNA
into the cell’s
DNA. The virus’
DNA then
controls the
cell’s DNA and
“tells” the cell to
make hundreds
of new viruses
which causes
the cell to burst,
releasing the
new viruses to
re-infect other
cells.
How Viruses Can Cause Mutations
When certain viruses attach to cell DNA, they can cause
misreading of nearby genes, damage nearby genes or cause
mis-copying of normal genes. This can make changes or
mutations in the host cell’s DNA.
Correcting Mutations With Gene Therapy
Gene therapy is an
attempt to replace
a faulty mutated
gene with a
healthy copy of
the normal gene.
At present it is a
risky therapy and
is only used for
diseases without
known cures.
Gene Therapy
A virus (like a cold
virus) is altered to
make it harmless and
a healthy gene is
inserted into the virus.
When the virus enters
the body and its DNA
attaches to a cell’s
DNA, the healthy gene
gets into the cell. The
cell then must
“switch on” the gene
to get the good
proteins needed.
End of Presentation