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Mutations
What is a mutation?
• Mutation – A change in the DNA that affects
inherited genetic information
• They may be gene mutations which result
from single gene changes, or chromosome
mutations.
• Mutations may be positive, negative or
neutral.
• Mutations drive evolution.
Mutagens
A substance that causes mutations.
• chemicals
• ionizing
radiation
• UV rays
• X-rays
GENE MUTATIONS
VOCABULARY
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Deletion/subtraction
Insertion/addition
(reading)frame shift
substitution
point mutations
Deletion (subtraction)
• If one nucleotide is removed, all the
codons from that point are changed.
(This results in different amino acids in the protein, which
may not be effective for its intended purpose.)
• This is known as a (reading frame shift)
a frame shift.
A deletion with no frame shift:
If a three-base codon is deleted, then
there is no frame shift, but there will still be
a problem with the protein formed. This is
what happens to cause the disorder
cystic fibrosis.
Cystic Fibrosis, or CF, is a common
fatal genetic disease.
CF is most common among people whose
ancestors came from Northern Europe.
The disease is caused by a recessive
allele on Chromosome #7.
Children with CF have serious digestive
problems. In addition, they produce a thick,
heavy mucus that clogs their lungs and
breathing passageways. The disease takes a
heavy toll. Only half of the children born with
Cystic fibrosis survive into their 20s.
a nebulizer which dispenses
medicine in a fine mist to
help thin mucus in the lungs.
HOW DOES DELETION CAUSE CF?
• A protein in the membrane of cells allows
chlorine ions (Cl-) to pass across biological
membranes.
• Most cases of CF involve a deletion of a
codon from the gene for this protein.
As a result, the protein does not fold properly.
Therefore it cannot be transported to the cell
membrane and is destroyed.
Because of this cells do not transport chlorine
ions properly and tissue throughout the body
malfunction
Cystic Fibrosis (1.5m)
Cystic Fibrosis Treatment (36s)
Man,37 Runs Marathon with Cystic
Fibrosis (3m13s)
Insertion (addition)
• The addition of a nucleotide changes the
codons, and therefore the amino acids in
the protein.
• A frame-shift occurs here as well.
SUBSTITUTION
• It effects one nucleotide. No frame shift
occurs. One or more bases are changed.
• A famous example is the substitution that
causes sickle-cell anemia.
Sickle cell anemia is a defect in the
hemoglobin of blood cells that causes then
to assume a sickle shape. This causes
clotting and organ damage. A person with
sickle-cell anemia may die as a young
adult.
The substitution that occurs in sickle-cell
anemia causes the amino acid valine to be
substituted for the amino acid gluatamic
acid in the hemoglobin protein.
Valine causes a portion
of the Red blood cell
to become hydrophobic
and twist out of
shape to avoid the
water in the blood plasma.
Substitutions are point
mutations
• A point mutation, or
single base substitution,
is a type of mutation that
causes the replacement
of a single base
nucleotide with another
nucleotide of the genetic
material.
Point Mutations can be:
• nonsense mutations:
code for the stop codon
• missense mutations:
code for a different
amino acid
• silent mutations (neutral) : code for the
same or a different amino acid but
without any functional change in the
protein
Chromosome mutations
• Deletion: loss of part of a chromosome
• Duplication: a repeated segment of a
Inversion: a portion of the
chromosome is reversed in its
orientation
Translocation: one part of a chromosome
breaks off and attaches to another nonhomologous chromosome.
Usually, two translocations happen at the
same time as the nonhomologous
chromosomes exchange portions.