What is meant by a ‘Lamp brush' chromosome? Explain its structure and functional significance. (UPSC 2017, 10 Marks, )

'लैम्प ब्रश' गुणसूत्र से क्या तात्पर्य है? इसके संरचना और कार्यात्मक महत्व की व्याख्या करें। (What is meant by a ‘Lamp brush' chromosome? Explain its structure and functional significance.)