How does antibiotic resistance illustrate natural selection in bacteria?

How does antibiotic resistance illustrate natural selection in bacteria?

• A. Antibiotics cause universal survival.
• B. Exposure kills susceptible, allowing resistant variants to survive and increase in frequency.
• C. Resistance arises only through horizontal gene transfer.
• D. Resistance can occur through random mutation and selection.

Answer: (B)

Antibiotics create a strong selective pressure on a bacterial population. Within that population there is variation in susceptibility—some bacteria carry resistance traits either by mutation or by acquiring resistance genes. When the antibiotic is present, the susceptible bacteria die or are inhibited, while the resistant ones survive and continue to reproduce. Their offspring inherit the resistance, so the trait becomes more common over generations. This shift in allele frequencies toward resistance is exactly how natural selection operates in action. While resistance can arise through mutation or gene transfer, the key point is that the antibiotic environment favors those with resistance, leading to an increasing proportion of resistant bacteria.

Antibiotics create a strong selective pressure on a bacterial population. Within that population there is variation in susceptibility—some bacteria carry resistance traits either by mutation or by acquiring resistance genes. When the antibiotic is present, the susceptible bacteria die or are inhibited, while the resistant ones survive and continue to reproduce. Their offspring inherit the resistance, so the trait becomes more common over generations. This shift in allele frequencies toward resistance is exactly how natural selection operates in action. While resistance can arise through mutation or gene transfer, the key point is that the antibiotic environment favors those with resistance, leading to an increasing proportion of resistant bacteria.