Final answer:
Genetic exchange allowing zoonotic viruses to infect humans is called antigenic shift, which is a significant change resulting from the reassortment of gene segments and can jump the species barrier.
Step-by-step explanation:
The genetic exchange in segmented viruses that allows a zoonotic virus to infect humans is termed antigenic shift. Unlike antigenic drift, which involves minor changes due to point mutations, antigenic shift is a major change that happens when there is a reassortment of gene segments. This often occurs when two different viruses infect the same host cell and exchange genetic material. The resulting virus can potentially be highly virulent and capable of jumping the species barrier to infect humans, sometimes leading to pandemics. The 2010 H1N1 swine flu outbreak is an example of a virus that emerged due to genetic reassortment between human and pig influenza viruses.