Question

In addition to vertical gene transfer, where genes/traits are passed down from a parent cell to daughter cells, prokaryotes can also acquire and transfer genes/traits through horizontal gene transfer. Name two different ways that this can happen, and describe how each one works.

Answer 1

Horizontal gene transfer: It is the transfer of genes from one bacteria to the other which are of same species or different species with the help of plasmids, transposable elements and bacteriophages.

In prokaryotes, horizontal gene transfer takes place in the following ways:

1. Transformation

2. Transduction

3. Conjunction

Here i am describing only 2 types of Horizontal gene transfer.

1. Transformation : It is a mechanism where a competent bacteria is ready to intake the exogenous material (foreign DNA) and alter its own DNA by combining and produces multiple copies. This process is called Transformation.

It may be naturally occuring or it may be artificially induced.

When a bacterial cell is dead and its gentic material/plasmid is transferred to the other bacteria cell where it combines with the DNA of the living cell and further it mutiplies and produces numerous recombination cell.

Industrially, this process helps in the synthesis of Antibiotics, Recombinant vaccines and Monoclonal antibodies in quantity.

2. Transduction : It is a mechanism where there is a tranfer of genetic material from one bacteria to the other with the help of Bacteriophages is known as transduction.

It may happen in two ways:

i. Generalised Transduction : It is characteristic of Virulent bacteriophages. In this method after phase attachment, phase DNA enters the DONOR cell and multiplies its gentic material and capsids. During assembling process, DONOR cell DNA fragments gets assembled in the phase. Donor cell undergo lysis and release bacteriophage.

After the release of bacteriophages, The Donor DNA engulfed bacteriophage may infect other bacteria and transfer the DONOR DNA to the new bacterial cell.

This may lead to recombination and form a Recombinant DNA with the help of DONOR DNA and RECIPIENT DNA.

ii. Specialized Transduction : It is a characteristic of temperate bacteriophage. In this process only restricted DNA genes are transferred from DONOR to the RECIPIENT cells.

Phase DNA with DONOR DNA gets integrated with the bacterial DNA and transfer to multiple generations. This is known as Lysogenic cycle. Prophases are seen.

When favourable conditions prevail, then phase undergoes lytic cycle.

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