The Nebenkern is a mitochondrial formation in the sperm of insects such as Drosophila. After the completion of meiosis, spermatid mitochondria wrap around each other to form a spherical aggregate, adjacent to the nucleus. [1] The Nebenkern proceeds to elongate into a double-stranded helical structure.[1][2] During flagellum elongation the Nebenkern unfolds and the two derivatives (major and minor mitochondrial derivatives) elongate down the bundle of microtubules that constitute the core of the flagellum[3]