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Mutations
Curly winged fruit flies
Drosophila, short leg
bassett hounds and
seedless grapes are all
examples of mutations
Mutations- definition
Mutation is a change or a mistake in DNA
replication. Mutations can arise in from
changes in individual genes or changes in
the arrangement of genes on a chromosome
Types of mutations
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1.
There are two types of genetic
mutations
Gene mutation
1.
2.
3.
2.
point mutation
chain termination mutation
frameshift mutation
chromosomal mutation
Point Mutation

A point mutation is a single base pair change
by physical or chemical means, where a
nucleotide is replaced by a different type.

A nucleotide can have a BASIC
SUBSTITUTION of a base pair.
Ex. Guanine changed to Adenine

Basic substitutions
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There can be three outcomes for a basic
substitution
1) silent mutation- NO EFFECT
–
–
ex. UCU, UCC, UCA, UCG are all the mRNA
code for Serine amino acid. These changes would
have no effect.
Also there are many genes which do not have an
effect on the body, a change in these genes
would not cause a change
Basic substitutions Cont.
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2) Neutral effect- A mutation that would
change the structure of the protein but have
little effect on its function
3) Drastic effect- a small change in one AA
would seriously effect the structure and
function of the protein
–
ex. Sickle cell Anemia- a change in one AA
changes the shape of the hemoglobin of the RBC
Deletion

A deletion is when nucleotide is left out of a
sequence of AA. Leaving out a nucleotide
will cause a shift in the DNA and result in a
synthesis of a polypeptide with an altered AA
sequence.
Point mutations
Insertion

Similar to deletion, a nucleotide inserted in a
sequence can cause a mutation in the
protein beyond the point of the extra
nucleotide.

In both deletion and insertion the polypeptide
formed by the mutated gene, if one can be
formed at all, is usually not functional.
Chain Termination Codon mutation

There are three codons ( Three base pairs)
that tell the AA to stop adding to the proteins
- UAA, UAG, UGA. When tRNA sees this
code it stops making the protein. If there is a
change in one of these codons it will have a
lethal effect since the protein will stop
growing or continue to grow.
Chromosomal mutations

Changes can occur in the
chromosome as well as in the
genes. Chromosomal mutations
can happen in different ways.

Ex. a piece of the chromosome
may break off or lost during
mitosis.

Some of the chromosomal
mutations can be repaired,
others repair themselves in
correctly.
Chromosomal mutations
Cancer
We now know that normal cells can be
transformed into malignant cancerous cells.
Gene mutations are ultimately to blame. Mutant
forms of genes, ONCOGENES, result in
abnormal proteins that disrupt the normal
reproduction of cells and cause cancer.
Oncogenes can be caused by a number of
ways- by carcinogens (cancer causing
substance (smoking, chemicals ); UV or X-rays
Cancer pictures
Mental retardation

A gene mutation responsible for a form of
mental retardation affecting one in 600 males
has been located on the X chromosome.
Mutation Disease- Sickle cell anemia

One in 500 people of African decent has
sickle cell anemia, which is a disease that
changes the shape of the hemoglobin
protein. There is just one nucleotide
difference in the sequencing of this protein.
These blood cells can block capillaries in the
body and cause pain, fever or even strokes
and paralysis. Most people don't live past 40
years of age.
Benefits of mutations

Although most people think of mutations as
harmful to or individual they can be helpful to
an organism. Mutations of genes is cause of
natural variation and one of the ways that
organisms evolve. Gene mutations can have
helpful results, allowing us to adapt to
changes in the environment and survive as a
species.
Examples of genetic diseases
-Inherited or mutation
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Acute intermittent
porphyria
adult polycyctic kidney
disease
albinism
alkaptonuria
BRCA breast cancer
cystic fibrosis
down syndrome
Duchenne muscular
dystrophy
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fragile x syndrome
hemophilia
Huntington disease
Neurofibromatosis
Phenylketonuria
Polyposis of the colon
Sickle cell Anemia
Tay-Sacs disease
Thalassemia