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  Mutation

Introduction to Mutation

In a species, differences are caused through the alterations in the environment or any alterations in the innate genetic setup of an organism or through the combination of both. Unexpected change in the genetical arrangement of an organism is described as mutation. In the year 1901, Hugo de Vries first employed the word mutation relies on his observation on Oenothera lamarckiana. Charles Darwin described these sudden changes as 'sports'. As per to Bateson, mutation is a discontinuous change. Relies on molecular basis of heredity, mutation is described as sudden alteration in the sequence of nucleotides of gene. The mutation carries about a change in the organism.  The organism that goes through mutation is known as a mutant. Example:- Oenothera lamarckiana.

Mutations that influence the biochemical reactions are known as biochemical mutations. For instance, biochemical mutants of Neurospora not capable to synthesize specific amino acids. A number of mutations drastically affect the genes and reason death to the individual. Such type of mutation is explained as lethal mutation. For instance, in the plant Sorghum, recessive mutant fails to generate chlorophyll and hence they die in the seedling stage. So, several of the mutations are injurious, since they disturb the genic balance of the organism. Even though most of the mutations are helpless and even harmful, and some of the mutations play an important role in the evolution of new species. Several new strains of cultivated crops and new breeds of domesticated animals are the products of gene mutations. Small seeded Cicer arietinum (bengal gram) unexpectedly get mutated to large seeded Cicer gigas is the case of gene mutation.

Classification of mutation

Mutations have been categorized in several ways based on dissimilar criteria. Depending on the type of cell where mutations take place, they are categorized into somatic and germinal mutation. They might be autosomal or sex chromosomal as per to their type of chromosome in which they take place. They might be spontaneous or induced as per to their mode of origin. They might be forward or backward as per to their direction. They might be dominant / recessive as per to their phenotypic expression of mutated genes.

Point or gene mutation

Point mutation is unexpected change in small segment of DNA either nucleotide pair or a single nucleotide. Gross mutation is an alteration including more than one or some nucleotides of a DNA.

The gene mutation might be introduced by loss or deletion of a nucleotide pair. This is known as deletion mutation and reported in a number of bacteriophages. Addition of one or more than one nucleotides into a gene results in addition mutation. Replacement of specific nitrogen bases through another base in the composition of DNA results in substitution mutation. The deletion and addition mutation change the nucleotide sequence of genes and finally result in the creation of defective protein and this leads to the death of the organism.  The substitution mutations can change the phenotype of the organism and comprise great genetic significance.

There are 2 kinds of substitution mutations -

1. transition and

2. transversion.

While a purine or a pyrimidine is changed by other purine or pyrimidine correspondingly this type of substitution is known as transition.

While a mutation includes the replacement of a purine for pyrimidine or viceversa this is known as transversion.

Mutagenic agents

The environmental situation and chemical substances that origin mutations in the organisms are known as mutagens / mutagenic agents. There are 2 types of mutagenic agents. They are:

1. Physical and

2. Chemical mutagenic agents.

Physical mutagenic agents

Electromagnetic radiation, radiations such as α and β, ϒ ultraviolet rays, temperature, etc. are a number of the instances for physical mutagens. X-rays and gamma rays are ionizing radiations that induce mutation in seeds. UV (ultra violate) rays are nonionizing radiations. Pollen can be treated along with UV (ultra violate) because pollen has germinal nucleus where mutation can be caused.

Chemical mutagenic agents

Chemicals can as well be employed for inducing mutations in the organisms. Such types of chemicals are known as chemical mutagenic   agents.

Example- Nitrous acid, Methyl   methane sulphonate (MMS) and ethyl methane sulphonate (EMS).  Ethyl methane sulphonate (EMS) has been widely employed for inducing mutations in microorganisms, higher plants and animals.

Significance of mutation

1. Mutations play a significant role in the origin of new species and works as a tool for evolution.

2. Induced mutations are helpful in agriculture, animal husbandry and biotechnology to generate new strains. For instance, mutant strains of Penicillium generate more penicillin.

3. Mutation is one of the best approaches for enhancement of crops.

4. Induced mutants are reported in wheat, soybeans, paddy, tomatoes, oats, and barley. Mutant ranges of wheat are early maturing, disease resistance and they are rich with protein.  Mutant varieties of paddy generate several tillers with long grains.

5. The learning of mutant strains of viruses assists us to make out the fine structure of gene. The genes are built up up of small functional units like cistron, recon and muton. Cistron is a unit of function, recon is the unit of recombination and muton is the unit of mutation.

6. Several types of mutations reason for heritable diseases and cancer in human beings.

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