Mutation

Mutation
Definition
Any change in the amount, structure and content of genetic material is called Mutations.
Mutations can appear in both sex chromosomes as well as in autosomes.
Types of Mutations
There are two main types of mutations.
1. Chromosomal Mutation
2. Gene Mutation
1. Chromosomal Mutation
The change in amount arrangement and the nature of genetic material on a chromosome is called Chromosomal mutations. It is also called Chromosomal aberration.

• This mutation is visible under the microscope.

Types of Chromosomal Aberration
There are following types of this mutation.
i. Deletion
ii. Duplication
iii. Inversion
iv. Translocation
i. Deletion
Definition
When a small portion of a chromosome is missing the situation is called Deletion.
Effects of Deletion
Pseudo-Dominance
Deletion may cause Pseudo dominance in heterozygous condition.
Lethal Effect
If deletion takes place in both homologous chromosomes then it has the lethal effect on the organism.
ii. Duplication
Definition
The repetition of a segment on a chromosome is called Duplication.
Effects of Duplication
Due to the duplication different physiological and morphological functions are disturbed.
iii. Inversion
Definition
When the arrangement of genes on a chromosome is changed then the mutation is called Inversion.
Effect of Inversion
Inversion reduced crossing over.
iv. Translocation
Definition
The transfer of a chromosomal segment to a non-homologous chromosomes is called Translocation.
Effect of Translocation
Translocation may give rise to varieties within species.
2. Gene Mutation
Definition
When small changes occur in the molecular structure of DNA, these are called Gene-Mutations.

• This mutations can not be detected by the microscope.
• These changes can produce drastic changes in the expression of the genetic messages.

Types of Gene Mutations
There are following types
i. Point Mutation
ii. Transposition
i. Point Mutation
Definition
The change of the sequence of one or a few nucleotides is called Point Mutation.
ii. Transposition
Definition
Individual genes may move from one place to another place on their own chromosome which is called Transposition.
Effects
This chromosomal rearrangement often brings alternation in the expression of the genes or that of neighboring genes.
DNA Damage (Causes of Mutation)
There are three major important causes of DNA damage, they are
1. Ionizing Radiation
2. Ultra Violet Radiation
3. Chemical Mutagens
1. Ionizing Radiation

• High energy radiations such as X-rays and Gamma rays are highly mutagenic Nuclear radiation is also of this sort.
• These radiations release unpaired electrons which are called free radical.
• These free radicals are highly reactive chemically, reacting violently with the other molecules of the cell including DNA.

2. Ultra Violet Radiation

• Ultra violet radiation is the component of sunlight.
• When molecules absorb UV radiation little damage is produce in these molecules.
• Mostly certain organic ring compounds are affected by UV-radiation.

3. Chemical Mutagens

• The chemicals which are capable of damaging DNA are called Mutagens.
• There are three main types of mutagens.
• Chemicals resembling DNA nucleotides but pair incorrectly when they are incorporated into DNA.
• Chemicals that remove the amino group form Adenine or cytosine, causing them to pair wrongly.
• Chemicals that add hydrocarbon group to nucleotide bases also causing them to pair wrongly.

Hereditary Diseases Due to DNA Damage
The two main hereditary disease due to DNA damage are
1. Sickle Cell Anaemia
2. Phenylketonuria
1. Sickle Cell Anaemia
An inherited autosomal recessive condition that causes abnormal haemoglobin in blood cells, leading to defective oxygen carrying, infections or organ damage is called Sickle Cell Anaemia.
Cause
The disorder occurs due to presence of abnormal haemoglobin (Glutamic acid is replaced by valine in β-chain at 5th position). It is produced due to mutation in gene. By the activity of changed gene abnormal haemoglobin is formed and sickle cell disease is produce.
Symptoms

• The abnormal haemoglobin has loco binding capacity with oxygen.
• The R.B.C containing the defective haemoglobin deform to a sickle shape during relative oxygen scarcity, haemoglobin molecules become insoluble and combine with one another forming stiff, rod like structures. Because of stiffness and irregular shape, these R.B.Cs may form clots blocking the small vessels.

2. Phenylketonuria
An inborn error of metabolism caused by the lack of an enzyme which breaks down amino acid phenylalanine, resulting in conversion of phenylalanine to other chemicals is called Phenylketonuria.
Causes
Phenylketonuria is a ressisive disorder caused by a mutant allele of the gene encoding the enzyme that normally breaks down phenylalanine. Only individual homozygous for the mutant allele development the disorder. It is because of the point mutation.
Symptoms

• The abnormal derivatives of phenylalanine are harmless because they interfere with the development of brain cells causing irreversible brain damage to the infants and can lead to severe, progressive mental retardation.
• Affective individuals rarely live for more than 30 years.

Treatment
It can be treated, if early detected by restricting the diet and avoiding phenylalanine.