Final answer:
The genre that consists of variations over a basso ostinato in Baroque music is the Passacaglia. It is similar to the Chaconne, with both featuring variations over a repeated bass line.
Step-by-step explanation:
The Baroque genre consisting of variations over a basso ostinato is the Passacaglia. This term is often used interchangeably with Chaconne, although some scholars make distinctions between the two. Both involve a series of variations over a repeated bass line or harmonic progression and are typical of the Baroque era, which showcases dramatic expression and complex forms.
The Fugue, another complex Baroque form, focuses on the interweaving of melodic lines rather than a basso ostinato. The Toccata is known for its virtuosic and improvisatory style, but does not fit the definition provided in your question.