All courses › Biology 1 › Antibiotic resistance

Antibiotic resistance

Natural selection changes how common heritable traits are in a population. The individuals do not choose to change. Mutations have already produced variation. When the environment changes, some have more offspring than others, and their alleles become more common. An antibiotic is such an environment. Bacteria that already happen to tolerate the substance survive and divide. The others die. Wrong use of antibiotics makes this selection stronger. The oldest traces of life are about 3.8 billion years old, so there has been plenty of time for such changes.

\text{variation} + \text{selection} + \text{inheritance}

evolution over generations

Symbols

mutation

source of new alleles

Example

Imagine 1000 bacteria of which 20 already tolerate the antibiotic.

That is $20/1000 \cdot 100 = 2$ %. After the treatment it is these that multiply.

The bacteria do not learn. Those that were already resistant were so before the antibiotic arrived.

Practise evolution for free →

← Carrying capacity · Species and the mule →

Part of Biology 1: Evolution.