Hint: Coiling of DNA helps in the packaging of DNA as it shortens the fibre and makes it compact. 2 m long DNA is coiled and is compacted in the cell. Two types of cell division are mitosis and meiosis. Both meiosis and mitosis have different types of coiling. Coiled up chromatin is known as the chromosome.
Complete answer: There are two types of coiling namely plectonemic and paranemic coiling. Plectonemic coiling is a type of coiling where two strands of chromatin coil with each other very tightly. Transcription is restricted in these regions because these strands are tightly coiled and require enough force to uncoil and without uncoiling, RNA polymerase is not able to act on these strands. This region appears darkly coloured under an electron microscope. The degree of coiling depends upon the length of the chromosome. Whereas in paranemic coiling, a little force is required to unwrap the chromatin threads, here, strands are easy to unwrap and transcription occurs in those regions. These regions are observed as light regions under an electron microscope. Plectonemic coiling occurs in mitosis and Paranemic coiling occurs in meiosis. DNA is coiled and shortened about sevenfold of its length which means that the DNA of 1 m long becomes 14 cm in its strings of bead.
Hence option D is the correct answer.
Note: Meiosis is also called the reductional division as it leads to the formation of haploid cells. It usually occurs in the germ cells of the body. Crossing over is an integral part of meiosis which leads to variations in offsprings.
