Chapter 17 Mastering Biology -Bio II

Part A - Interpreting a phylogenetic tree The phylogenetic tree shows the hypothesized evolutionary relationship between the variant strains of H1N1 virus. Each branch tip is one variant of the H1N1 virus with a unique HA gene sequence. The more closely connected two variants are, the more alike they are in terms of HA gene sequence. Each fork in a branch, called a node, shows where two lineages separate due to different accumulated mutations. The number of nodes separating two variants is an indication of how many DNA sequence differences there are between the variants, thus how distantly related they are. Referring to the phylogenetic tree in Figure 1, which variant is more closely related to A/Taiwan1018/2011 in group 9 (brown): A/Taiwan/552/2011 or A/Taiwan/8542/2009? (For help reading the phylogenetic tree, see the hint.)

A/Taiwan/552/2011; variants 1018/2011 and 552/2011 share a more recent common ancestor than is shared with variant 8542/2009. You can see from the tree that A/Taiwan1018/2011 and A/Taiwan/552/2011 share a more recent common ancestor than A/Taiwan1018/2011 and A/Taiwan/8542/2009 do. The branch length from the node connecting the former pair is shorter than the branch length from the node connecting the latter pair.

Part C - Interpreting a graph The scientists also graphed the H1N1 isolates by the month and year of isolate collection, which reflects the time period in which each viral variant was actively causing illness in people. Select Figure 2 from the drop-down menu above the phylogenetic tree (Figure 2) . The graph shows the number of isolates collected from ill patients (one isolate per patient) on the y-axis and the month and year that the isolates were collected on the x-axis. Each group of variants is plotted separately with a line color that matches the phylogenetic tree diagram. Which group of variants was the earliest to cause H1N1 flu in over 100 patients in Taiwan?

Group 7 (black line)

Cycle A is the _____ cycle and cycle B is the _____ cycle.

Lyctic...lysogenic The lytic cycle concludes with rupture of the host cell. The lysogenic cycle involves replication of viral DNA along with replication of the host.

Once a group of variants had a peak number of infections, did members of that same group cause another wave of infection?

No, each group of variants caused only one wave of infection. Correct These results support the researchers' hypothesis that newly evolved H1N1 variants were responsible for each new wave of the flu outbreak.

How do prions, which are misfolded proteins, infect organisms?

Prions enter brain cells and cause normal forms of the protein to refold into the prion form. Prions are a misfolded version of a protein normally found in the brain. When prions come into close proximity with the normal proteins, they cause them to refold into the prion form.

Groups 9, 10, and 11 all had H1N1 variants that caused a large number of infections at the same time in Taiwan. Does this mean that the scientists' hypothesis, that new variants cause new waves of infection, was incorrect? Explain your answer. Their hypothesis was incorrect; the graph clearly shows three distinct peaks occurring in the same wave. Their hypothesis was still supported; each of these three groups has a different height peak. Their hypothesis was still supported; these three groups arose along different lineages but emerged to cause illness during the same wave. Their hypothesis was incorrect; all three groups are rooted in the same phylogenetic tree but caused three distinct peaks in the same wave.

Their hypothesis was still supported; these three groups arose along different lineages but emerged to cause illness during the same wave. All three groups had variants that were genetically distinct from the variants that caused the earlier infection waves. These three groups just happened to cause serious infection at the same time.

How do prions differ from viruses? Select all that apply.

Unlike a virus, a prion is a single molecule. Unlike viruses, prions do not include any nucleic acids. Unlike viruses, prions are infectious proteins. Select All.

One variant in the green groups (Groups 1, 3, and 6) was used to make a vaccine that was distributed very early in the pandemic. Based on the graphed data, does it look like the vaccine was effective? Why or why not?

Yes, it was effective; the green line never reaches 100 on the y-axis.

The lytic cycle of bacteriophage infection ends with the _____.

rupture of the bacterium The bacterium ruptures and phages are released.