Download Genetic Mutations

Compiled by Siti Sarah Jumali
Room 14, Level 3
06-4832123
Changes in Heredity- Mutations
Nothing is perfect…
Mutation – any changes (alterations) in the sequence of
DNA that affects genetic information and the
appearance of offspring.
Caused by: UV Light, X-Rays, etc.
Types of Mutations
Gene mutation – a mutation that occurs in a single
gene and affects one trait.
Ex: Eye color, Sickle cell Anemia, Hemophilia
Chromosome mutation – a mutation that occurs in
many genes and affects many traits at once.
Ex: Down Syndrome (an extra 21st chromosome)
How Can Mutations Affect an
Organism?
Body cell mutations can cause cancer.
- only the individual is affected.
Gamete cell mutations affect the egg
and the sperm.
- all offspring of the individual can
be affected.
Gene Expression
An individual’s trillions of body cells all come from one
cell (zygote).
In differentiation the cells become different tissues. (ex:
skin, muscle, organ)
Certain cells will “turn on” or activate only the genes
they need. This is called gene expression.
Factors that Affect Gene Expression
The internal and external environment of a cell can
influence which genes are “turned on”.
Ex: - Hormones can “tell” a cell to activate a
specific gene.
- Outside temperature changes fur color in
rabbits.
End of Today, You Should Know:
 What is a mutation?
 What are some examples of harmful mutations?
 Neutral Mutations are…
 What are some examples of beneficial mutations?
What is a Mutation?
 Abrupt, heritable changes in a single gene or a region
of a chromosome, can also include alterations in
chromosome number
 Mutations are the fuel for evolution and are the basis
for the variation in population.
What is a Mutation?
 Can be when one letter is switched - accidentally
copied incorrectly within the DNA.
 When one section of the DNA, sometimes an
entire gene, is not properly connected to the rest
of the DNA; sometimes it even reconnects to
another chromosome
 One section of DNA, sometimes an entire gene,
appears more than once
What is a Mutation?
 Will only get passed on to offspring when the sex cells
contain the mutation
 Can be caused after birth by environmental factors
like radiation and chemicals, which can alter a
person’s DNA, even in their sex cells, causing their
offspring to have disorders
Mutation..
 Affects molecular changes in the DNA sequence of a gene
 Alter the coding sequence within a gene
 Causes permanent change in DNA sequence
 Involve insertion or removal of 1 or more base pairs
 Point mutation is a change in single base pair within DNA
sequences
 Base substitution changes is in pair
 2 types of changes
 Transition (within same group AT and GC)
 Transversion (between 2 groups)
Transition vs Transversion
Changes in coding sequence
 Silent mutation –does not alter the amino acid sequence of
the polypeptide although the nucleotide sequence was
changed
 Missense mutation- base substitution causes change in
amino acid eg sickle cell anemia (Glu to Val)
 Nonsense mutation – change from normal to stop codon.
Translation is termination in abrupt producing truncated
protein
 Frameshift mutation – additional or deletion of a number
of nucleotides that will not be realized if 3 nucleutides
because 3 bases code for 1 aa. But if it is not in multiple 3,
will be very dangerous, changes the whole aa sequence
Missense
mutation
Nonsense
mutation
Silent or neutral mutation
 Silent mutation can result in enhancing new protein,
but all other mutations reduce the function
 Missense mutation generally affect mutation, it is also
known as neutral mutation
Silent
mutation
Frameshift mutation
Frameshift
mutation
Down’s Syndrome
• Offspring receives 3 copies of 21st chromosome
 90% of the time the extra chromosome comes from
the mother
 Affects 1 in 800 live births
Effects of Down’s Syndrome
 Different in each person
 Does not usually pass this onto children
 Common effects include
 Learning Disabilities
 Heart defects (can usually be corrected with modern
technology)
Turner’s Syndrome
 45 (instead of 46) chromosomes
 offspring are born with one X chromosome (no Y; only
one X)
 only affects women
 In about 80% of cases the X comes from the mother
and the father’s sperm has no Y
 Affects 1 in 2500 live births
Effects of Turner’s Syndrome
• Sometimes a lack of ovarian development
• Can have more masculine qualities (stronger),
although are female
 In some cases:
 Webbed neck
 Arms that turn in at the elbow
 Low hairline on the back of the head
Klinefelter’s Syndrome
• Offspring inherit a Y chromosome and two X
chromosomes
 Because there is a Y all offspring are male
 Sometimes the extra X comes from the egg and
sometimes it comes from the sperm
 Occurs in 1 out of every 500 – 1000 live births
Effects of Klinefelter Syndrome
 Sparse facial and body hair
 Underdeveloped muscles
 Wide hips
 Tall height
 Long legs & arms
 Higher-pitched voice
Albinism
 Caused by a recessive gene
 Causes genes to release unusual amounts of melanin
(chemical that provides color)
 Affects 1 in 17,000 people
 People of all races are susceptible
 All animals are susceptible
Effects of Albinism





Light skin
Light hair
Reddish or violet eyes (in some albinos)
Lack of eye pigment leads to vision problems
Skin cancer – especially in third world countries
There are MANY other mutations…
Not all
Mutations
Are Bad…
Mutations Can Be Neutral
 They may have little or no effect on the survival of
an organism or on its ability to reproduce.
 They may result in the same kind of organism -
meaning that the change still tells the cell to do
what it should, so there is no difference.
 It is estimated that the average human has 50-100
mutations within their DNA - most (if not all) are
neutral or beneficial
Mutations Can Be Beneficial
 Bacterial resistance to antibiotics
 Insecticide resistance in bugs
 Rapid mutation rates in virus’s proteins allowing them
to adapt to new “hosts”
Mutations Can Be Beneficial
 In humans, it can be a different set of
circumstances… Here’s an example:
 Sickle-Cell Anemia is a genetic disorder in
which there is a defect in the structure of red
blood cells. This leads to fatigue and anemia
when not treated.
 However, it has been found that people who are
carriers for Sickle-Cell Anemia also has some
genetic protection against another disease,
malaria.
Mutations
Can
Be
Beneficial
• In evolutionary studies, scientists have
connected the presence of a brain chemical
microcephalin (a proposed mutation) with the
human’s development of art, music, and
complex tool-making practices
• This same research indicates that the human
brain is still evolving and becoming more and
more capable of more complex tasks
• Some humans have been found to have
mutations that protect them from other
diseases, such as AIDS