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  Mechanism of Genetic Variation and Hereditary, Biology tutorial

Introduction:

Each and every living organism looks like its ancestors in most of its features. The maintenance of particular properties, that is, the constancy of characters over generations is termed as heredity.

Genetics is basically the study of inheritance (that is, heredity) and the variability of the features of an organism. Inheritance exacts transmission of genetic information from parents to their progeny (that is, offspring). DNA (Deoxyribonucleic acid) is the chemical substance responsible for the hereditary in all the cells as it beams the genetic information. Each and every genetic character can be assigned to a gene that carries the information. Microorganisms are able of transmitting the genetic information from generation to generation having great precision.

Genetic Variation:

This is changes in or of a gene that leads to a loss of the enzymes or to the production of an altered enzymes, therefore, to recognizable modifications in the hereditary character.

Genetic variation in bacteria can occur through:

  • Mutation
  • Gene transfer or recombination

Mutation:

Mutation can be stated as the change in nucleotide series of DNA.  Mutation can comprise the addition, deletion or substitution of the nucleotides. These modifications in the nucleotides are stable and heritable and are passed down from one generation to the next. Mutation introduces genetic variation amongst organisms.

A mutant is a strain of any cell or virus carrying a change in the nucleotide sequence. 

A mutant is dissimilar from its parent strain in:

a) Genotype:  The nucleotide series of the genome.

b) The Phenotype:  The observable property of the mutant in the modified phenotype is termed as a mutant phenotype.

The strain isolated initially from nature is termed as the wild kind strain.

Mutation can take place spontaneously or induced beneath the affect of external agents (that is, mutagens).

1) Spontaneous Mutation:

This is a kind of mutation which takes place without exposure to external agents or any known mutagenic treatment. It takes place at a fairly constant frequency in a specific organism, one per 106 to 1010 in a population derived from the single bacterium. It might outcome from errors in the DNA replication or from the action of mobile genetic molecules termed as transposons.

2) Induced Mutation:

A mutation is any change in a DNA sequence which can be passed from parent to offspring. By using inducing mutations, scientists have been capable to raise genetic variation that breeders based on to produce crops having desirable traits like resistance to insects and diseases.

Dissimilar to recombinant DNA methods, induced mutation doesn't add any foreign genetic material to the plant.

Basically, it produces results which could have occurred via naturally occurring mutations and choosing of desirable progeny. Though, as mutations take place naturally at low frequencies and arbitrarily in the DNA, it would need much more time to accomplish such outcomes.

Mutations can be induced in a diversity of ways, like by exposure to ultraviolet or ionizing radiation and chemical mutagens.

Types of Mutation:

Two common kinds of mutation are: point mutation and frame shift mutation.

a) Point Mutations:

Point mutations take place as a result of the replacement of one nucleotide for the other in particular nucleotide series of a gene or defined as change in just one base pair.

Point mutations in protein: coding genes can influence protein structure and are named according to if and how they modify the encoded protein.

b) Frame Shift Mutations:

These mutations result from the loss or addition of one or more nucleotides in a gene and are known insertion or deletion mutations correspondingly.

This outcome in a shift or the reading frame.

Frame shift mutations generally are much harmful and yield mutant phenotypes resultant from the synthesis of the non-functional protein.

Genetic Recombination: 

This is the formation of a new genotype through reassortment of genes following the exchange of genetic material among two different chromosomes which encompass similar gene at corresponding sites and are from the different individuals. Offspring or Progeny from recombination have combination of genes dissimilar from those which are present in the parents. In bacteria, genetic recombination's outcome from three kinds of gene transfer, they are:

a) Conjugation: This is the transfer of genes among cells which are in physical contact having one another.

b) Transduction: This is the transfer of genes from one cell to the other by a bacteriophage.

c) Transformation: This is the transfer of cell free or naked DNA from one cell to the other.

Mechanism of Recombination:

Within the recipient cell, the donor DNA fragment is positioned along the recipient DNA in such a manner that homologous genes are adjacent. Enzymes act on the recipient DNA, causing nic and excision of a fragment. The donor is then integrated to the recipient chromosome in place of the excised DNA. The recipient becomes the combination cell as its chromosomes have DNA of both the donor and the recipient cell.

Conjugation:

This is a method of genetic transfer which comprises cell to cell contact. It is plasmid encoded mechanism that is; it is controlled by gene taken by certain plasmid (like F plasmid). The process of conjugation comprises a donor cell that contains conjugative plasmid and a recipient cell which doesn't.

Transformation:

This is a genetic transfer procedure by which free DNA is incorporated to a recipient cell and brings about the genetic change. Some prokaryotes are naturally transformed comprising certain species of Gram negative and Gram positive bacteria and a few species of Archaea due to the DNA of prokaryotes is present in the cell as a large single molecule, if the cell is gently lysed, the DNA pours out and breaks simply into fragments having genes that are discharged into the surrounding atmosphere. When a fragment contacts a competent cell, a cell which is capable to take up DNA and be transformed, the DNA can be bound to the cell and taken in.

Transduction:

This is a method of genetic transfer in which a bacterial virus (that is, bacteriophage) transfers DNA from one cell to the other. Virus can transfer the host genes in two manners: 

  • generalized transduction
  • specialized transduction

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