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3. Chromosomal mutations. These mutations involve changes
to the structure or number of chromosomes. Examples include
deletions, duplications, inversions, and translocations.
Introduction to mutations
Types of mutations
Effects of mutations
Mutagens
Human genetic disorders
Evolution and mutations
Biotechnology and mutations
Introduction to Mutations
Causes of mutations
Mutations can be caused by a variety of factors, including:
1. Spontaneous errors during DNA replication. The DNA
replication process is not perfect, and errors can occur
spontaneously. These errors can result in a change in the DNA
sequence, leading to a mutation.
2. Environmental factors. Exposure to certain environmental
factors such as radiation, chemicals, and viruses can cause
mutations in DNA. For example, ultraviolet (UV) radiation from
the sun can cause mutations that lead to skin cancer.
3. Inherited mutations. Mutations can also be inherited from
parents. When mutations occur in the germ cells (sperm and egg
cells), they can be passed down to offspring and can cause
genetic disorders.
4. Replication errors during cell division. During cell division,
DNA is replicated and distributed to the daughter cells. Errors
during this process can result in mutations.
5. Mutagenic agents. Some chemicals and substances, known
as mutagens, can cause mutations in DNA. Examples of
mutagens include tobacco smoke, certain pesticides, and
industrial chemicals.
A mutation is a change in the DNA sequence that can occur
spontaneously or be caused by exposure to certain
environmental factors known as mutagens. Mutations can occur
in any cell of an organism and can be inherited or arise
spontaneously during an individual's lifetime.
A gene mutation is a change in the DNA sequence that makes
up a gene. This can result in a change in the amino acid
sequence of a protein, which can affect the protein's function.
Gene mutations can occur naturally or be caused by
environmental factors such as radiation, chemicals, or viruses.
Types of mutations
6. DNA damage repair errors. Cells have mechanisms to repair
damaged DNA, but errors in these mechanisms can lead to
mutations.
7. Insertions and deletions. These mutations involve the
addition or removal of one or more nucleotides in the DNA
sequence, which can alter the reading frame and change the
amino acid sequence of the protein.
Gene mutations can affect an organism differently depending on
the specific mutation and its location within the genome. Some
mutations may have no effect, while others can lead to genetic
disorders or an increased risk of developing certain diseases.
1. Point mutations. These are the most common type of
mutation, and they involve a change in a single nucleotide (A, T,
C, or G) in the DNA sequence.
Point mutations are divided into three categories:
● Silent mutations. These mutations do not change the
amino acid sequence of the protein encoded by the
DNA because of the redundancy of the genetic code.
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Missense mutations. These mutations change one
amino acid in the protein sequence. Depending on the
location of the mutation, this may or may not affect the
protein's function.
Nonsense mutations. These mutations change a
codon that normally encodes an amino acid into a stop
codon, leading to premature termination of protein
synthesis.
2. Frameshift mutations. These mutations occur when
nucleotides are inserted or deleted from the DNA sequence,
causing a shift in the reading frame of the codons. Frameshift
mutations can have significant effects on the resulting protein's
function.
Effects of mutations
Mutations can affect an organism's phenotype differently, from
neutral to beneficial or harmful.
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Neutral mutations. These mutations have no effect on
an organism's phenotype or health. For example, a
change in the DNA sequence that does not alter the
amino acid sequence of a protein.
●
Beneficial mutations. These mutations can provide
an advantage to an organism, such as resistance to a
disease or an increased ability to survive in a particular
environment.
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Harmful mutations. These mutations can cause harm
to an organism, such as a genetic disorder or an
increased risk of developing cancer.
MUTAGENS
Mutagens are chemical or physical agents that can cause
changes or mutations in the DNA sequence of an organism.
These mutations can have a variety of effects, including
changes in the organism's traits, genetic disorders, and cancer.
Examples of chemical mutagens include:
● Polycyclic aromatic hydrocarbons (PAHs) found in
tobacco smoke and charred meat
● Nitrosamines found in processed meats and tobacco
smoke
● Benzene, a common industrial chemical
● Aflatoxins produced by fungi in food crops like
peanuts and corn
● Vinyl chloride, a chemical used in plastic production
Examples of physical mutagens include:
● Ionizing radiation, such as X-rays and gamma rays
● Ultraviolet (UV) radiation from the sun or artificial
sources like tanning beds
● Electromagnetic radiation, such as radio waves and
microwaves
● High-energy particles, such as those found in cosmic
radiation and nuclear fallout
Mutagens can cause cancer by inducing mutations in genes that
control cell growth and division, leading to uncontrolled cell
growth and the formation of tumors. For example, a mutation in
the tumor suppressor gene TP53 can prevent cells from properly
regulating their own growth, leading to the development of
cancer. Some mutagens can also damage DNA directly, leading
to the formation of abnormal or damaged proteins that can
interfere with normal cellular functions.
HUMAN GENETIC DISORDERS
Human genetic disorders are caused by mutations in the DNA
sequence that can affect the function of genes and proteins.
These mutations can be inherited from parents or arise
spontaneously during development.
2. Huntington's disease. It is a genetic disorder caused by
mutations in the HTT gene, which codes for a protein called
huntingtin. Mutations in HTT can cause the accumulation of
abnormal proteins in the brain, leading to the progressive
degeneration of nerve cells and cognitive decline.
3. Sickle cell anemia. It is a genetic disorder caused by
mutations in the HBB gene, which codes for the beta-globin
subunit of hemoglobin, a protein that carries oxygen in red blood
cells. Mutations in HBB can cause the formation of abnormal
hemoglobin molecules, leading to the characteristic sickle shape
of red blood cells and anemia.
4. Cri du chat Syndrome. It is a genetic disorder caused by a
deletion of a portion of chromosome 5 causes it. This deletion
can affect gene expression in brain development, leading to
intellectual disability and delayed development. It can also affect
the development of the larynx, resulting in a high-pitched cry that
sounds like a cat.
5. Down syndrome. It is a genetic disorder caused by an extra
copy of chromosome 21. This extra chromosome can lead to
overexpression of genes on chromosome 21, affecting the
development of the brain, heart, and other organs. The
characteristic facial features of Down syndrome may be due to
altered gene expression during facial development.
6. Edward syndrome. It is a genetic disorder (Trisomy 18)
caused by the presence of an extra copy of chromosome 18.
This extra chromosome can disrupt normal development,
leading to severe intellectual disability and physical
abnormalities. Many of the features of Edward syndrome are
thought to be due to the dysregulation of genes on chromosome
18.
1. Cystic fibrosis. It is a genetic disorder caused by mutations
in the CFTR gene, which codes for a protein that regulates the
movement of salt and water in and out of cells. Mutations in
CFTR can lead to the buildup of thick mucus in the lungs and
other organs, causing respiratory and digestive problems.
7. Jacobsen syndrome. It is a genetic disorder caused by
deleting a portion of chromosome 11. This deletion can affect
gene expression in brain development, leading to intellectual
disability and delayed development. It can also affect the heart's
and other organs' development, resulting in physical
abnormalities.
8. Klinefelter syndrome. It is a genetic disorder caused by the
presence of an extra X chromosome in males. This extra
chromosome can affect the production of testosterone, leading
to reduced levels of this hormone and infertility. The physical
and developmental features of Klinefelter syndrome may be due
to altered gene expression resulting from the extra X
chromosome.
9. Turner syndrome. It is a genetic disorder caused by the
absence of all or part of one X chromosome in females. This
missing chromosome can affect the development of the ovaries
and other organs, leading to infertility and physical abnormalities
such as short stature. The characteristic features of Turner
syndrome may be due to altered gene expression resulting from
the missing X chromosome.
Human karyotyping is the process of analyzing the number,
size, and shape of chromosomes in a person's cells.
Chromosomes are structures that contain an individual's genetic
material in the form of DNA. Humans have 23 pairs of
chromosomes, for a total of 46 chromosomes
Genetic testing and counseling can help individuals and
families understand their risk of developing or passing on
genetic disorders. Genetic testing involves analyzing a person's
DNA to detect mutations or other genetic variations that may
increase the risk of a particular disorder.
EVOLUTION AND MUTATION
Karyotyping is typically done using cells from a blood sample,
although other types of cells, such as skin cells or amniotic fluid
cells, may also be used. The cells are first treated with a
chemical that stops them in the dividing stage of the cell cycle.
Then, the cells are stained with a dye that highlights the
chromosomes and allows them to be visualized under a
microscope.
Mutations are the ultimate sources of genetic variation, which
is the raw material for evolution. Mutations can lead to evolution
by introducing new genetic traits into a population. Over time,
natural selection can act on these traits, leading to changes in
the genetic makeup of the population.
When a mutation occurs, it can create a new allele (a variant
form of a gene) that was not previously present in the population.
This can increase genetic variation within the population. If this
new allele confers a beneficial trait, individuals carrying that
allele may be more likely to survive and reproduce, passing
the beneficial trait to their offspring. This process is called
natural selection, and it can lead to the spread of the
advantageous allele in the population.
On the other hand, if a mutation creates a harmful allele,
individuals carrying that allele may be less likely to survive and
reproduce. This can lead to the removal of the deleterious
allele from the population over time through a process called
negative selection.
The chromosomes are then arranged in pairs according to their
size, shape, and banding patterns, numbered from 1 to 22 based
on their size (with chromosome 1 being the largest) and labeled
X and Y for the sex chromosomes. Normal human karyotype
should show 23 pairs of chromosomes, with the sex
chromosomes being either XX (female) or XY (male).
Karyotyping can be used to detect chromosomal
abnormalities, such as aneuploidy (an abnormal number of
chromosomes), or structural abnormalities, like translocations,
deletions, or duplications. This can be helpful in diagnosing
genetic disorders like Down syndrome, Turner syndrome, or
Klinefelter syndrome.
●
Translocations occur when a piece of one
chromosome breaks off and attaches to another
chromosome. This can result in a change in the
position of certain genes, which can affect their
expression and potentially lead to genetic disorders.
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Deletions occur when a portion of a chromosome is
missing, either due to a break in the chromosome or
failure of a chromosome to separate properly during
cell division. Deletions can range in size from small to
very large and can lead to a variety of genetic
disorders, depending on which genes are affected.
●
Duplications occur when a section of a chromosome
is duplicated, resulting in an extra copy of that
segment. Duplications can be inherited from a parent
or can occur spontaneously during cell division. Like
deletions, duplications can range in size and can have
varying effects on gene expression and development.
Genetic variation is important for evolution because it provides
the raw material for natural selection to act upon. Without
genetic variation, natural selection would not be able to favor
certain traits over others, and evolution would not occur.
A dominant gene is a gene that expresses its phenotype
(observable trait) when present in either one or both copies of
the gene. A recessive gene is a gene that expresses its
phenotype only when present in both copies of the gene.
BIOTECHNOLOGY AND MUTATION
Biotechnology is the application of technology to study,
manipulate and modify biological systems, including living
organisms, cells, and molecules. One of the major areas of
biotechnology is genetic engineering, which involves modifying
the genetic material of living organisms to produce new products
or improve existing ones.
HUMAN KARYOTYPING
GENETIC ENGINEERING
Genetic engineering is the process of manipulating the genetic
material of an organism, often by introducing or modifying
specific genes. This process can involve introducing new
genetic material from a different organism or modifying an
organism's existing DNA to produce a desired trait or
characteristic.
For example, scientists can use gene editing technologies like
CRISPR-Cas9 to precisely target and modify specific genes in
an organism's DNA, introducing or removing mutations in the
process. This can be used to create new crop varieties that are
more resistant to pests or environmental stresses or to develop
new treatments for genetic diseases by correcting specific
mutations that cause the disease.
Genetic engineering relies on the ability to manipulate DNA,
which can be achieved through a number of techniques,
including CRISPR-Cas9 technology, gene therapy, and
others. CRISPR-Cas9 technology is a powerful tool that
enables scientists to precisely target and edit specific genes
within an organism's DNA, allowing for the creation of
genetically modified organisms with desirable traits or the
correction of genetic disorders.
Gene therapy is another form of genetic engineering that
involves the delivery of functional copies of genes into cells
to correct genetic defects or diseases. This technology is still in
its early stages, but it holds promise for treating a variety of
genetic disorders, such as cystic fibrosis, muscular dystrophy,
and sickle cell anemia.
Recombinant DNA (rDNA) is a type of DNA that is artificially
created by combining DNA molecules from different sources.
This technology involves the use of enzymes called restriction
endonucleases to cut DNA molecules at specific locations,
allowing for the insertion of new DNA sequences from other
sources helps them understand the concept of gene mutation
and its implications.
CHECK YOUR UNDERSTANDING:
Name: __________________________
Grade and Section: _______________
Test 1. Complete the following table:
DNA
ACT CTG AAT TAA CTA
coding
DNA
template
mRNA
tRNA
Amino
Acid
ATG
GGT
3. A DNA strand that originally reads 5’-GATATC-3’ undergoes
a mutation that changes it to 5’- GATCATC-3’. This is an
example of what type of mutation?
A. Deletion
B. Insertion
C. Nonsense mutation
D. Point mutation
4. What type of point mutation results in a frameshift mutation?
A. Deletion
B. Insertion
C. Substitution
D. Both A and B
5. Which is NOT a type of substitution mutation?
A. Conservation
B. Missense
C. Nonsense
D. Silent
6. Which is an example of a stop codon in RNA?
A. UAG
B. UAA
C. UGA
D. All of the above
7. Which type of mutations can result in a frameshift?
A. Nonsense and missense
B. Nonsense and insertions
C. Insertions and deletions
D. Missense and deletions
8. Which type of mutation does NOT change the overall function
of the protein?
A. Insertion
B. Missense
C. Nonsense
D. Silent
9. Which type of mutation results in the replacement of one
nucleotide by another?
A. Insertion
B. Missense
C. Nonsense
D. Silent
10. Which of the following is not an example of a point mutation?
A. Frameshift mutation
B. Missense mutation
C. Nonsense mutation
D. Silent mutation
TEST 3. Match the following
DNA
coding
DNA
template
mRNA
tRNA
Amino
Acid
CTG
CGA
ATA
TCA
CAA
ATC
GGT
TEST 2. Encircle the letter of the correct answer
1. Frameshift Mutations are generally much more serious and
often more deadly than point mutations.
A. True
B. False
C. Depends upon the condition of the DNA
D. It is much more serious but not deadly
2. Frameshift mutations are the result of what occurrence?
A. Insertions or deletions that are not a multiple of three.
B. A mutation that changes an amino acid codon to a stop codon
C. A mutation that changes one amino acid to another.
D. A nucleotide-pair substitution