What type of genetic variation occurs when bacteria uptake external DNA?

The correct answer is transformation, which refers to a process in which bacteria acquire external DNA from their environment. This can happen through the uptake of free DNA that might be released by other bacteria when they die or through various forms of DNA present in their surroundings.

Transformation leads to genetic variation because the new DNA can be integrated into the bacterial genome, potentially giving the bacteria new traits, such as antibiotic resistance or new metabolic capabilities. This mechanism of genetic exchange is particularly significant in bacteria as it allows for rapid adaptation and evolution within a population.

In contrast, transduction involves the transfer of genetic material between bacteria through bacteriophages (viruses that infect bacteria), and mutation refers to changes in the DNA sequence that occur due to errors in replication or external factors. Replication is the process by which DNA is copied to produce new cells and does not involve the incorporation of external DNA. Each of these processes contributes to genetic variability within microbial populations, but transformation specifically emphasizes the uptake of external DNA.