Which of the following is commonly utilized as a vector for gene cloning in higher organisms?

Explanation

Retroviruses are frequently employed as vectors to introduce genetic material into higher organisms due to their ability to integrate into the host genome. In contrast, baculoviruses are mainly used for gene expression in insect cells, Salmonella typhimurium is a bacterial species not typically used as a cloning vector, and Rhizopus nigricans is a fungus unrelated to vector systems.