When a pig is simultaneously infected with an avian influenza strain and a human influenza strain, the two sets of genes present in the pig result in antigenic shift (option b).
Explanation:
Antigenic shift occurs when two different strains of a virus meet in an organism and combine to produce a new type of virus containing a mixture of the surface antigens of the strains that have combined.
Once two virus of different strains coexist in an organism they lose their viral capsid, exposing the genetic information that will be transcribed in the host cell into a different virus, containing the combination of the surface antigens of the viruses that were found in the mentioned organism.
<em>The other options are not correct because mainly </em><em><u>genetic drift</u></em><em> refers to changes in the antigens of a virus due to repeated random mutations in the viral genome.</em>
