Polytene Chromosomes

Polytene chromosomes are large chromosomes that are visible under a microscope. They are formed when multiple DNA strands join together and elongate. They are usually found in the salivary glands of invertebrates such as Drosophila, and are important for geneticists to study the structure and organization of genes. Polytene chromosomes are also useful for understanding the effects of environmental and genetic factors on gene expression and for identifying potential disease-causing loci. Additionally, they have been used to study gene duplication, mutation, gene regulation, and to identify molecular markers associated with genetic diseases.