Question

Appearance of antibiotic resistant bacteria is an example of
A. Adaptive radiation
B. Transduction
C. Pre-existing variation
D. Divergent evolution in the population.

Answer 1

We all know that normal bacterial colonies died in the presence of some particular antibiotics. But they can survive in the presence of that particular antibiotic due to some mutations or chemical change.

Complete answer:
Bacterial colony → In presence of antibiotics → Dies
Mutated Bacterial colony (survived from the wild type) → in presence of antibiotics → survive (multiplication)

In this case wild type bacteria do not adapt to the mutant variation so they will die in presence of antibiotics. So here the appearance of antibiotic-resistant bacteria is not involved and the option is wrong.
Transduction is a method of genetic material transfer. So in this case antibiotic-resistant bacteria do not transfer any genetic materials. So it is the wrong option.
In antibiotic-resistant bacteria, mutant genes spread through the bacterial population and become multiplied and overspread. These mutant genes were previously present in some of the wild type bacterial colonies. So we can say that this is the example of pre-existing mutation and mutation is also called variation so the right option is Pre-existing variation.
Here Divergent evolution in the population is not present because we cannot see any homology relationship between wild type bacteria and the mutant type bacteria.

The correct answer is option C.

Note:
Points to be remember:
In antibiotic-resistant bacteria, they are mutated bacterial colonies.
They are derived from the wild type bacteria. Here we are not introducing any kind of genetic changes or mutation to the wild type bacterial colony, mutated genes are present previously in those wild type bacterial colonies.
These mutated genes are resistant to the antibiotics that mean they can survive in presence of antibiotics and the whole bacterial population becomes resistant.
Some examples of antibiotic-resistant bacteria that are resistant to antibiotics include methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Enterococcus, etc.