Final answer:
Transformation is the uptake of extracellular DNA by a cell, changing its genotype, and is a key process in horizontal gene transfer.
Step-by-step explanation:
The modification of a genome via external application of DNA originating from a separate genotype is called transformation. Transformation, or horizontal gene transfer (HGT), is the uptake and expression of extracellular DNA by a cell. This process is naturally responsible for the spread of traits such as antibiotic resistance within a bacterial population. Other mechanisms of horizontal gene transfer include conjugation and transduction. Whereas transduction is the transfer of genetic material from one bacterium to another by a phage, conjugation involves the direct transfer of DNA through physical contact between cells.