Download course: bio 201

NAME: AKALABU, MAUREEN CHIDINMA.
MATRIC NO: 14/SCI03/003
DEPERTMENT: BIOCHEMISTRY
COURSE: BIO 201
MUTATION A CURSE OR A BLESSING.
What is mutation?
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.
Gene mutations can be classified in two major ways:
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Hereditary mutations are inherited from a parent and are present throughout a person’s life in
virtually every cell in the body. These mutations are also called germ line mutations because they are
present in the parent’s egg or sperm cells, which are also called germ cells. When an egg and a
sperm cell unite, the resulting fertilized egg cell receives DNA from both parents. If this DNA has a
mutation, the child that grows from the fertilized egg will have the mutation in each of his or her
cells.
Acquired (or somatic) mutations occur at some time during a person’s life and are present only in
certain cells, not in every cell in the body. These changes can be caused by environmental factors
such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself
during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells)
cannot be passed on to the next generation.
Classification of mutation
By effect on structure
Mutations in the structure of genes can be classified as:
Small-scale mutations: such as those affecting a small gene in one or a few nucleotides, and this
comprises of; Point mutations, often caused by chemicals or malfunction of DNA replication, Point
mutations that occur within the protein coding region of a gene may be classified into three kinds,
depending upon what the erroneous codon codes for -Silent mutations, which code for the same (or a
sufficiently similar) amino acid, Missense mutations, which code for a different amino acid, Nonsense
mutations, which code for a stop codon and can truncate the protein.
Insertions: add one or more extra nucleotides into the DNA.
Deletions: remove one or more nucleotides from the DNA.
Large-scale mutations: in chromosomal structure; and this includes;
Amplifications (or gene duplications) leading to multiple copies of all chromosomal regions, increasing
the dosage of the genes located within them.
Deletions of large chromosomal regions, leading to loss of the genes within those regions.
By effect on function: and these includes;
Loss-of-function mutation, gain-of-function mutation, dominant negative mutation (antimorphic
mutation), lethal mutation, and back mutation.
By effect on fitness: A harmful, or deleterious, mutation decreases the fitness of the organism.
A beneficial or advantageous mutation increases the fitness of the organism.
A neutral mutation has no harmful or beneficial effect on the organism.
A nearly neutral mutation is a mutation that may be slightly deleterious or advantageous, although most
nearly neutral mutations are slightly deleterious.
By impact on protein sequence.
By inheritance.
Types of mutation
Deletion: genetic materials are removed or deleted.
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.
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.
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.
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.
Point: A single base change in DNA sequence.
Frameshift: 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.
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 rejoin exons in the mRNA. A
change in these sequences can eliminate splicing at that site which would change the reading frame and
protein sequence.
Translocation: A structural abnormality of chromosomes where genetic material is exchanged between
two or more non-homologous chromosomes.
Mutation could be both advantageous and disadvantageous.
In the following fields:Advantages: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.
Malaria resistance
Individuals with sickle cell, as a result of mutation, have been observed to portray malaria resistance.
Generally, this is a harmful mutation since sickle blood cells are not as effective as normal cells in their
functioning. In regions where there are increased cases of malaria, this mutation is favourable as
individuals with blood cells that are sickle shaped are not likely to contract malaria.
Disadvantages.
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.
Diseases-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.
Sickle-Cell Anemia Sickle-cell anemia is not contagious; no one can catch it from another person. The
only way to contract the disease is to inherit it from one's parents. It manifests itself as a defect in the
shape of red blood cells that interferes with their ability to transport oxygen to other cells in the body.
Normal red blood cells are doughnut-shaped. In persons suffering from sickle-cell anemia, the cells are
shaped like a half-moon or sickle, hence the disease's name. These sickle-shaped cells are unstable and
break apart easily, clogging or damaging blood vessels, leading to pain, lung damage, and, in some cases,
heart and brain damage as well.
Having said all these we can conclude that mutation is a curse!!!!