The story of a butterfly that explains how species evolve.

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People often wonder or rather doubt how new species are formed. Some people doubt the whole phenomenon of evolution because it's "a theory of evolution". However, in reality, evolution happens and we can find evidence of it in nature. Here, for instance, a species of butterfly in Amazon region was found to have evolved from the hybridization of two other species of butterflies. Interestingly, the descendants of all these three lineages of butterflies coexist in same geographical region and two of these occasionally mate with each other.
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The COVID-19 is not caused by artificially engineered virus

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In recent days, I have seen a few forwarded videos explaining how the current pandemic of COVID-19 caused by corona virus SARS-CoV-2 is pre-planned attempt of China to harm the economies of several countries. Although these people give evidence of chronological events supporting their theories, but scientific investigation of the SARS-CoV-2 genome easily refutes their claims. A correspondence published in Nature Medicine journal by Kristian G. Anderson and collegues from The Scripps Research Institute, USA explain how unlikely it is that the SARS-CoV-2 virus has been engineered or has escaped from lab.




The SARS-CoV-2 virus spike protein (shown in diagram) is responsible for attachment of virus to human cells. the spike protein, as shown in the diagram is made of two subunits. Subunit S1 has the receptor binding domain. A polybasic cleavage site (PCS) is present at the junction of the two subunits of the spike protein.
 
Receptor binding domain (RBD)
The receptor binding domain of the spike protein is the region which attaches to angiotensin converting enzyme 2 (ACE2) receptor in human cells and provides an entry point to the virus into human cells. ACE2 is expressed in lung tissue which is the major entry point of the virus. The strength of the interaction between viral RBD and human ACE2 determines how infectious the virus is. The researchers have shown that the SARS-CoV-2 RBD has strong affinity to human ACE2. It also has affinity toward ferret and cat ACE2. The sequence of RBD in SARS-CoV-2 is very different from the sequence of RBD in SARS-CoV which caused SARS epidemic earlier. Also, the RBD sequence is not ideal for binding human ACE2. Had the virus been engineered in lab for causing epidemic, the RBD sequence chosen would have been the optimal sequence predicted by current software. Thus, the current virus may have evolved naturally.

 Polybasic Cleavage Site (PCS)
Earlier studies on coronaviruses have shown that PCS acquisition in spike proteins have increased the virulence. The PCS sequence in SARS-CoV-2 is predicted to cause O-linked glycosylation in structurally adjacent amino acid residues of the spike protein. Both the PCS sequence and O-linked glycans are unique to SARS-CoV-2.  Coronaviruses isolated so far from bats and pangolins do not have the PCS. These organisms are believed to be the origins of the current virus strain. The researchers postulate that the PCS might have been acquired after transmission of the virus into humans or there might be currently unsampled coronavirus strains circulating in wild populations of these animals. 

 Also, it is unlikely that the virus had accidentally escaped from some lab as no closely related virus has been reported yet. The acquisition of PCS requires passage of virus with human ACE2 which again is not reported in literature. The development of predicted O-linked glycans requires the presence of an immune system during the viral propagation.
Based on all thee observations, we can understand that the current pandemic is not caused by artificially engineered cornovirus.







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