Polytene chromosomes of Drosophila salivary glands each consist of multiple identical DNA strands that are aligned in parallel structures. How could these arise?

Polytene chromosomes may be defined as the giant chromosomes that contain alternate dark and light bands when view under the microscope. These chromosomes are found in the salivary gland of Drosophila.

These glands are functionally highly active and contain thousand of DNA strands. These chromosomes are aligned parallel with each other as the replication is normal but the cells are unable to separate and fails to undergo the process of cytokinesis.