Which is an example of genetic engineering?

The correct answer is the production of an oral vaccine naturally in fruit, as this represents an application of genetic engineering. Genetic engineering involves the manipulation of an organism's DNA to exhibit desired traits or produce specific biological products. In the case of oral vaccines produced in fruit, scientists can insert specific genes from a virus into the DNA of the fruit, allowing it to produce antigens which can stimulate an immune response when consumed. This innovative technique showcases how genetic engineering can create safe and effective vaccines through biotechnological methods.

The other options do not directly illustrate genetic engineering as clearly. Rapid amplification of DNA sequences typically refers to polymerase chain reaction (PCR), a technique for copying DNA rather than altering it. The application of an orthopoxvirus does not generally involve genetic modification but rather the use of a virus for medical purposes or research. Breeding two dog species, while it involves selective breeding, does not constitute genetic engineering in the way that modifying the DNA of an organism directly does.