1. Retroviruses like HIV use an enzyme called reverse transcriptase to produce DNA copies of their RNA genomes so they can integrate into the host cell's DNA. 2. Reverse transcriptase is also used in molecular biology to make DNA copies of mRNA transcripts in order to study and manipulate genes. 3. Gene therapy aims to treat genetic diseases by inserting normal genes into patients' cells, either to complement recessive alleles or override dominant disease-causing alleles. However, it carries risks like harming patients or diseases developing.