1) so viruses from the same type can undergo antigenic shift. and it happens when two strains from the same type of virus but different strains infect the same host cell. and a new combination of the virus is made. Influenza is a common virus type that undergoes antigenic shift. When an influenza strain from one organism transfers to another organism this is called zoonosis and there is a high chance that the virus will undergo antigenic shift if that organism is also infected at that time and they both have different strains AND it infects the same host cell.
2) A structure can become vestigial when an organism is no longer subjected to the selection pressures that originally maintained its function. Over time, if the structure is no longer advantageous or necessary for survival due to changes in the environment or the development of a new, more efficient mechanism (through natural selection), it may lose its original function and become vestigial.
3) so emigration effects the gene pool. if an organism moves from a population, the population that it moved from will be affected (as an allele is lost so, that gene pool of that population will will therefore decrease as the genetic diversity decreased AND the gene pool is really affected especially when that organism had rare alleles) but the population that it moved to will not be affected unless if it does interbreed and produce a viable fertile offspring then yeah the genetic diversity will increase and that will play a role in the gene pool (basically bigger gene pool).
4) Yes, the folding of hierarchical structures is an essential part of protein synthesis and is specifically related to the process of a protein achieving its final functional form. After a protein is synthesized through translation, it undergoes a series of folding steps to acquire its proper three-dimensional structure (tertiary structure determines its function) which determines its function.
