Question

Analysis of the phylogeny of flu viruses reveals that the two 1968 strains (see the accompanying figures) both carry neuraminidase N2, but their hemagglutinins are distantly related (H2 and H3). Moreover, before the global pandemic of 1968, human flu viruses had never carried H3. This observation suggests that ________.

1) H3 was acquired from a nonhuman strain which, in turn, allowed the virus to infect humans on a global scale

2) flu strains, when present together in the same host cell, can trade genes

3) the 1968 human flu strain acquired its H3 gen from a bird virus

4) All of these conclusions are supported by this data.

Answer 1

The 1968 influenza strains carrying neuraminidase N2 and distinct hemagglutinins H2 and H3 suggest the introduction of H3 from a nonhuman strain, gene trading between flu strains in a host, and the acquisition of H3 from a bird virus, all conclusions supported by the data and the concept of antigenic shift.

Step-by-step explanation:

Analysis of the phylogeny of flu viruses indicates that the two 1968 strains both carry neuraminidase N2, but their hemagglutinins (H2 and H3) are distantly related. Given that human flu viruses had not carried H3 before the global pandemic of 1968, the evidence suggests that:

1. H3 was acquired from a nonhuman strain which, in turn, enabled the virus to infect humans on a global scale.
2. Flu strains, when present together in the same host cell, can trade genes.
3. The 1968 human flu strain likely acquired its H3 gene from a bird virus.

All three conclusions are supported by the data. This notion aligns with the understanding that through antigenic shift, which involves the mixing of the genes of two different influenza viruses, new influenza strains emerge that can have pandemic potential, often marked by new hemagglutinin types, such as H3.