Which graph best represents directional selection? Graph A has trait value on the horizontal axis and population of individuals on the vertical axis. The original population increases, decreases, increases, and then decreases again. The population after selection increases at the point that the original population drops. Graph A Graph B has trait value on the horizontal axis and population of individuals on the vertical axis. The original population and population after selection have similar curves, but the original population peaks before the population after selection. Graph B Graph C has trait value on the horizontal axis and population of individuals on the vertical axis. The original population peaks at the same time as the population after selection but the original population peaks higher and at a more rapid speed. Graph C

In 1959, doctors began using the powerful antibiotic methicillin to treat infections of staphylococcus aureus, but within two years, methicillin-resistant strains of s. aureus (mrsa) appeared. how did the resistant strains of s. aureus emerge? in 1959, doctors began using the powerful antibiotic methicillin to treat infections of staphylococcus aureus, but within two years, methicillin-resistant strains of s. aureus (mrsa) appeared. how did the resistant strains of s. aureus emerge? staphylococcus aureus bacteria that were able to synthesize cell walls using a protein that was not affected by methicillin survived the methicillin treatments and reproduced at higher rates than did other individuals. over time, these resistant individuals became increasingly common. in response to treatment of staphylococcus aureus infections with methicillin, some bacteria began to synthesize cell walls using a protein that was not affected by methicillin. these bacteria survived the methicillin treatments and reproduced at higher rates than did other individuals. over time, these resistant individuals became increasingly common. in response to treatment of staphylococcus aureus infections with methicillin, bacterial populations gradually began to synthesize cell walls using a protein that was not affected by methicillin.