Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be present in an individual pig at the same time. When this occurs, it is possible for genes from bird flu virus and human flu virus to be combined. If the human flu virus contributes a gene for Tamiflu resistance (Tamiflu is an antiviral drug) to the new virus, and if the new virus is introduced to an environment lacking Tamiflu, then what is most likely to occur?

If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency.

Explanation:

The new virus will be resistant to Tamiflu. The Tamiflu resistance gene will become common in the environment due to directional selection. Directional selection can be described as a condition in which one phenotype is favoured such that the phenotype becomes abundant in an area and hence the allele frequency of the area changes. This occurs because that phenotype is better adapted to survive in an environment.