In two communities of similar size and age structure (a and b) there were outbreaks of viral illness (virus a in community a and virus b in community b), both of which were traced back to a single source. exposure to these viruses in each community confers permanent immunity. in community a, 200 susceptible people were exposed to an index case, 150 people were infected (not including the index case), 75 people became ill, and 40 people died. in community b, pathogenicity was 40%, infectivity was 90% and virulence was 60%.a. which virus had the greatest infectivity? b. which virus was most pathogenic? c. which virus was most virulent?

Keeping in mind the life cycle of bacteriophages, consider the following problem: during the reproductive cycle of a temperate bacteriophage, the viral dna inserts into the bacterial chromosome where the resultant prophage behaves much like a trojan horse. it can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. as stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?

What pattern of migration do whales follow?

Which would be the most useful source of evidence to support mcneill's contention?