Define "genetic engineering."

Genetic engineering refers to the manipulation of an organism's DNA to alter its characteristics. This process can involve various techniques, including the insertion, deletion, or modification of genes within an organism's genome, resulting in desired traits that may not occur naturally. This can be used in a variety of fields, such as agriculture to create pest-resistant crops, in medicine for gene therapy to treat genetic disorders, or in research to improve our understanding of gene functions.

The other choices, while related to genetics, do not accurately define genetic engineering. The creation of synthetic genes falls under a specific aspect of genetic engineering but does not encompass the broader manipulation of DNA. The study of heredity and variation refers to genetics as a science, rather than the practical application involved in genetic engineering. Lastly, natural selection is an evolutionary process explaining how organisms adapt over time through differential survival and reproduction, which is distinct from the direct manipulation of genes performed through genetic engineering.