Segmented viruses are capable of undergoing genetic reassort…

Segmented viruses are capable of undergoing genetic reassortment when they infect a host cell.  A.  Explain how genetic reassortment can occur to cause antigenic shift in a virus.  B.  This is the process that can produce unique viruses such as the H1N1 strain of Influenza that contains human, avian, and swine influenza genetic material.  Why are these new viruses such a threat to us?