Final answer:
The novel influenza H7N9 strain is a result of viral reassortment, which is when genes from two different influenza viruses mix within a host cell to create a new strain. (option 1)
Step-by-step explanation:
The novel influenza virus (H7N9 strain) is believed to be a result of a process called antigenic shift, which is a form of genetic recombination or reassortment. This occurs when two different influenza viruses infect the same host cell and their genes mix to create a new virus with a different combination of spike proteins. This mixing of genes from different viruses can result in a highly virulent strain that humans may have no immunity against, as seen with the H7N9 strain that emerged in China in 2013. Viral reassortment is a major change in spike proteins due to gene reassortment, and it is one of the mechanisms of antigenic variation in influenza viruses. With the antigenic shift, the resultant virus possesses a mixture of the proteins of the original viruses, which can lead to the emergence of new influenza strains.
The novel influenza virus (H7N9 strain) is believed to be a result of a process called viral reassortment (option 1).