Download BIO201_1

NAME: AFON AGNES ADEOLA.
COLLEGE: SCIENCES.
DEPARTMENT: BIOCHEMISTRY.
MATRIC NO: 14/SCI03/002
LEVEL: 200.
MUTATION A CURSE OR A BLESSING?
WHAT IS MUTATION?
A mutation is a permanent alteration of the nucleotide sequence of
the genome of an organism, virus, or extra chromosomal DNA or
other genetic elements. Mutations result from damage to DNA which
is not repaired, errors in the process of replication, or from the
insertion or deletion of segments of DNA by mobile genetic elements.
Mutations may or may not produce discernible changes in the
observable characteristics (phenotype) of an organism. Mutations play
a part in both normal and abnormal biological processes including:
evolution, cancer, and the development of the immune system,
including junction diversity.
Mutation can result in many different types of change in sequences.
Mutations in genes can have no effect, alter the product of a gene, or
prevent the gene from functioning properly or completely. Mutations
can also occur in no genic regions. One study on genetic variations
between different species of Drosophila suggests that, if a mutation
changes a protein produced by a gene, the result is likely to be
harmful, with an estimated 70 per cent of amino acid polymorphisms
that have damaging effects, and the remainder being either neutral or
weakly beneficial. Due to the damaging effects that mutations can
have on genes, organisms have mechanisms such as DNA repair to
prevent or correct mutations by reverting the mutated sequence back
to its original state. Mutation is a natural process that changes a DNA
sequence. And it is more common than you may think. As a cell
copies its DNA before dividing, a "typo" occurs every 100,000 or so
nucleotides. That's about 120,000 typos each time one of our cells
divides. Most commonly, a single base is substituted for another.
Sometimes a base is deleted or an extra base is added. Fortunately, the
cell is able to repair most of these changes. When a DNA change
remains unrepaired in a cell that will become an egg or a sperm, it is
passed down to offspring. People commonly use the terms "mutant"
and mutation" to describe something undesirable or broken. But
mutation is not always bad. Most DNA changes fall in the large areas
of the genome that sit between genes, and usually they have no effect.
When variations occur within genes, there is more often a
consequence, but even then mutation only rarely causes death or
disease. Mutation also generates new variations that can give an
individual a survival advantage. And most often, mutation gives rise
to variations that are neither good nor bad, just different.
WHAT CAUSES MUTATION?
Mutations can be caused by external (exogenous) or
endogenous (native) factors or they may be caused by errors in the
cellular machinery. Physical or chemical agents that induce mutations
in DNA are called mutagens and are said to be mutagenic.
Exogenous factors: environmental factors such as sunlight, radiation,
and smoking can cause mutations.
Endogenous factors: errors during DNA replication can lead to
genetic changes as can toxic by-product.
Almost all mutations are either neutral or bad. "Bad" meaning they
decrease the health and/or survivability prospects of the recipient of
said mutation. Generally, if a mutation is noticeable, it would be what
we refer to as a "birth defect" or a "genetic disease."
Evolution depends on these, and life would have never progressed
beyond some sort of simple self-catalysing chemical reaction if not
for these positive mutations. But positive mutations even those of the
adaptive nature are extremely rare compared to flat-out bad mutation.
So, it's great that mutations have allowed us to evolve to what we
are. But you'd probably like for your child to have as few mutations as
possible, because the chances of a mutation being in any way positive
one are pretty much negligible. On the other hand, the likelihood of
that mutation being a birth defect are, sadly, not at all negligible of
cellular metabolism.
TYPES OF MUTATION.
There are several classes of mutations described below. The original
sequence is shown on the top with the mutated sequence below it. The
genetic sequence is shown in black while the protein sequence is in
blue. Changes in sequence are highlighted by yellow. To see what
these mutations look like when sequenced,
1. Deletion Genetic material is removed or deleted. A few bases can
be deleted (as shown on the left) or it can be complete or partial loss
of a chromosome (shown on right).
2. Frame shifts the insertion or deletion of a number of bases that is
not a multiple of 3. This alters the reading frame of the gene and
frequently results in a premature stop codon and protein truncation.
3. Insertion When genetic material is put into another region of
DNA. This may be the insertion of 1 or more bases, or it can be part
of one chromosome being inserted into another, non-homologous
chromosome.
4. Missense A change in DNA sequence that changes the codon to a
different amino acid. Not all missense mutations are deleterious, some
changes can have no effect. Because of the ambiguity of missense
mutations, it is often difficult to interpret the consequences of these
mutations in causing disease.
5. Nonsense A change in the genetic code that results in the coding
for a stop codon rather than an amino acid. The shortened protein is
generally non-function or its function is impeded.
6. Point A single base change in DNA sequence. A point mutation
may be silent, missense, or nonsense.
7. Silent A change in the genetic sequence that does not change the
protein sequence. This can occur because of redundancy in the genetic
code where an amino acid may be encoded for by multiple codons.
8. Splice Site A change in the genetic sequence that occurs at the
boundary of the exons and introns. The consensus sequences at these
boundaries signal where to cut out introns and re-join exons in the
mRNA. A change in these sequences can eliminate splicing at that
site which would change the reading frame and protein sequence.
9. Translocation
A structural abnormality of chromosomes
where genetic material is exchanged between two or more nonhomologous chromosomes.
ADVANTAGES OF MUTATION.
1. Survival.
Mutations have allowed humans to adapt to their environment. For
instance, lactose tolerance is a specific external mutation that was
advantageous in societies that raised cows and goats. Mutations have
been responsible for antibiotic resistance in bacteria, sickle cell
resistance to malaria, and immunity to HIV, among others. A rare
gene mutation leading to unusual shortness of height has proven to be
advantageous for a particular Ecuadorian community. National Public
Radio's (NPR) Jon Hamilton writes how the Ecuadorian community
with the rare gene mutation known as Larson syndrome are protected
against cancer and diabetes.
2. Diversity.
In 2008, Professor Eiberg from the Department of Cellular and
Molecular Biology stated, “Originally, we all had brown eyes but a
genetic mutation affecting the OCA2 gene in our chromosomes
resulted in the creation of a 'switch,' which literally 'turned off' the
ability to produce brown eyes.” He explains that things like “hair
colour, baldness, freckles, and beauty spots” are all brought about by
mutations.
DISADVANTAGES OF MUTATION.
1. Disease.
As much as mutations have helped humans, mutations are also the
cause of certain diseases. For instance, E! Science News 2008
explains how a particular mutation relatively common on the Indian
subcontinent predisposes people to heart disease. Many other
diseases, such as cancer, diabetes and asthma, are linked to genetic
mutations. E.g Albinism.
2. Genetic Disorder.
A genetic disorder is a disease that is caused by an abnormality in an
individual's DNA. Abnormalities can range from a small mutation in a
single gene to the addition or subtraction of an entire chromosome or
set of chromosomes.” Non-disjunction is one of the most common
types of mutations. Down syndrome is a non-disjunction and a
common genetic disorder that has other consequences such as
developmental delays.
CLASSIFICATION OF MUTATION.
1.By effect on structure
The sequence of a gene can be altered in a number of ways. Gene
mutations have varying effects on health depending on where they
occur and whether they alter the function of essential proteins.
2. by effect on fitness
3. by inheritance
4. by impact of protein synthesis.