A mutation is the permanent alteration of the
nucleotide sequence of the genome of an organism,
virus, or extra chromosomal DNA or other genetic
elements.
Mutations result from errors during DNA replication
or other types of damage to DNA
The two main causes of mutation are
• Mistakes in Cell Replication
• Environmental Factors
MISTAKES IN CELL REPLICATION
During replication of DNA, double strands of DNA are
separated. Each strand is then copied to become another double
strand. About 1 out of every
100,000,000 times, a mistake
occurs during copying, which can
lead to a mutation.
ENVIRONMENTAL FACTORS
Mutations can also be caused by environmental
foes. Tobacco, ultraviolet light and other
chemicals (Hydroxylamine
Base analogs etc ) Alkylating agents are all
potential enemies of DNA.
These agents cause the DNA to break down.
This is not necessarily unnatural — even in the
most isolated and pristine environments, DNA
breaks down.
CHROMOSOMAL GENE MUTATION
MUTATION
i. POINT MUTATION
i. DELETION SILENT
ii. DUPLICATION MISSENSE
iii. INVERSION NONSENSE
iv. TRANSLOCATION ii. FRAMESHIFT MUTATION
INSERTION
DELETION
CHROMOSOMAL
MUTATION
A chromosome aberration, or mutation is a missing, extra, or irregular
portion of chromosomal DNA. It can be from an atypical number of
chromosomes or a structural abnormality in one or more chromosomes.
There are many types of chromosome anomalies. They can be organized
into two basic groups, numerical and structural anomalies.
i. Numerical disorders
This is called aneuploidy (an abnormal number of chromosomes), and
occurs when an individual either is missing a chromosome from a pair
(monosomy) or has more than two chromosomes of a pair
(trisomy, tetrasomy etc.). In humans, an example of a condition caused
by a numerical anomaly is Down Syndrome, also known as Trisomy 21
DOWN
SYNDROME
Q. WHAT IS DOWN SYNDROME ?
Down syndrome is a chromosomal disorder caused by an error in cell
division that results in an extra 21st chromosome. The condition leads
to impairments in both cognitive ability and physical growth.
Q .HOW DO YOU HAVE A BABY WITH DOWN
SYNDROME ?
Down syndrome is typically caused by what is called nondisjunction.
Nondisjunction happens when a pair of chromosomes fails to separate
during egg (or sperm) formation. When that egg unites with a normal
sperm to form an embryo, the embryo ends up with three copies of
chromosome 21 instead of the normal two.
TURNER SYNDROME
Turner syndrome (TS) also known
as 45,X, is a condition
in which a female is partly
or completely missing an
X chromosome.
Turner syndrome is due to a
chromosomal abnormality in which
all or part of one of the X
chromosomes is missing or altered. While most people
have 46 chromosomes, people with TS usually have 45.
ii. Structural abnormalities
When the chromosome's structure is altered, this can
take several forms:
1. DELETION
2. DUPLICATION
3. INVERSION
4. TRANSLOCATION
A portion of the chromosome is
duplicated, resulting in extra
genetic material
Duplications arise from an event
termed unequal crossing-over that
occurs during meiosis between
misaligned homologous
chromosomes.
A portion of the chromosome has broken
off, turned upside down, and reattached,
therefore the genetic material is inverted.
Chromosome
translocation is
caused by
rearrangement of parts
between nonhomologous
chromosomes.
A gene mutation is a permanent alteration in the
DNA sequence that makes up a gene, such that
the sequence differs from what is found in most
people.
Mutations range in size; they can affect
anywhere from a single DNA building block (base
pair) to a large segment of a chromosome that
includes multiple genes.
POINT MUTATION
A point mutation is a type of mutation that causes a single
nucleotide base substitution, insertion, or deletion of the
genetic material, DNA or RNA.
Causes of point mutations
• Point mutation is a random SNP (single-nucleotide
polymorphism) mutation in the DNA.
• A single point mutation can change the whole DNA
sequence.
• Point mutations may arise from
spontaneous mutations that occur during DNA replication.
The rate of mutation may be increased by mutagens
Functional categorization
Nonsense mutation:
Code for a stop, which can truncate the protein. A
nonsense mutation converts an amino acid codon into a
termination codon. This causes the protein to be
shortened because of the stop codon interrupting its
normal code.
Missense mutation:
It is a point mutation in which a single nucleotide change
results in a codon that codes for a different amino acid.
It is a type of nonsynonymous substitution
.
Silent mutations:
Code for the same amino acid. A silent mutation has no
effect on the functioning of the protein. A single
nucleotide can change, but the new codon specifies the
same amino acid, resulting in an unmutated protein. This
type of change is called synonymous change, since the
old and new codon code for the same amino acid.
FRAMESHIFT MUTATION
A frameshift mutation (also called a framing error or a
reading frame shift) is a genetic mutation caused by
indels (insertions or deletions) of a number of
nucleotides in a DNA sequence that is not divisible by
three.
DELETION MUTATION
Deletion mutation is a mutation in which
a part of a chromosome or a sequence of DNA
is lost during DNA replication.
Deletions can be caused by errors in
chromosomal crossover during meiosis ,
which causes several serious genetic
diseases. e.g. Williams syndrome.
Small deletions are less likely to be fatal;
large deletions are usually fatal
INSERTION MUTATION
Insertion mutation is the addition of one or more
nucleotide base pairs into a DNA sequence.
Insertions can be particularly hazardous if they occur in
an exon, the amino acid coding region of a gene
