A type of chromosome found in the oocytes of many vertebrate and invertebrate animals, notably newts and other amphibians, and in the giant single-celled alga Acetabularia. It is characterized by having numerous loops arising from the long axis of the chromosomal arms. Under the microscope this gives an appearance reminiscent of a cylindrical brush of the type formerly used for cleaning oil lamps. The loops are regions where the chromosome is uncoiled and the DNA exposed for active transcription by an associated matrix of RNA and proteins. This arrangement enables the transcription of greater amounts of RNA compared with normal prophase chromosomes.