Question

Where do viruses come from?

Answer 1

Hint: Viruses are the simplest infective organism consisting of a nucleic acid (DNA or RNA ) and a protein coat or envelope. They remain dead outside the cell and come into life by infecting the host. There is a $3$ hypothesis regarding the development of the virus. The evolutionary study prevails on the origin of the virus as an organism.

Complete answer:
The $3$ hypothesis regarding the origin of the virus are as follows :
Progressive or escape hypothesis – This hypothesis states the origination of the virus utilizing progression. The main concept was that the mobile genetic elements gained the ability for cell to cell movement. If we look into the infection of the retrovirus into the host cell we can see retrovirus(contains ss RNA) uses reverse transcriptase enzyme to form the double-stranded DNA that is transferred to the host nucleus and with the help of integrase it binds to the host genome. The viral genes are now transcribed and translated and hence the formation of new viral proteins. This process is seen to mirror an important component of the eukaryotic genome known as the retrotransposons.
Regressive hypothesis – This theory states the origin of the virus using a regressive process. The theory depends upon the evolution of viruses from more complex or free-living organisms. The organisms lose their genetic information as they evolve and become parasitic. The nucleocytoplasmic large DNA virus (NCLDVs) is best for this hypothesis. This concept was based mainly on the evolution of certain obligate intracellular parasites including Chlamydia from the free-living ancestors.
The Virus- First Hypothesis: Both the progressive and regressive hypothesis is based on the appearance of cells first. Viruses existed from the precellular era and were self-replicating. They became complex and organized along with time. Eventually, various enzymes required for the cell membrane and other organelles production gradually came.

Note:
None of the above-mentioned theories are correct. The arouser of the virus can be through different mechanisms. The virus can be classified based on the genetic material present. The Single-stranded positive RNA virus (coronavirus), single-stranded negative RNA(Rhabdovirus), double-stranded RNA virus (Reovirus), Single-stranded DNA virus (Parvovirus), double-stranded DNA virus (Herpesvirus).