Question

What are polytene chromosomes and how are they formed?

Answer 1

Hint: A chromosome is a long DNA molecule that contains part or all of an organism's genetic material. Most eukaryotic chromosomes contain histones, which, with the help of chaperone proteins, bind to and condense the DNA molecule to keep it intact.

Complete answer:
Polytene chromosomes are massive chromosomes that are commonly found in insects’ salivary glands. In 1881, Balbiani discovered polytene chromosomes. They are also known as salivary gland chromosomes because they were discovered in the salivary glands. They're called polytene because they have a lot of chromonemata.
They are formed when chromosomes are duplicated repeatedly without being separated. Endomitosis is the medical term for this condition. They have darkly stained bands and the region between two bands is lightly stained and is known as interband. The polytene chromosome is approximately 0.5 mm long and 20 m in diameter. Dipteran flies, unicellular protozoans, and other organisms with polytene chromosomes are examples.
After 10 rounds of DNA replication, the salivary gland of Drosophila contains about 1000 DNA molecules. Each polytene chromosome in Chironomus contains around 16000 DNA. Somatic pairing occurs in polytene chromosomes, which means homologous chromosomes remain side by side. Polytene chromosomes expand the cell and increase its volume. Due to multiple copies of the genes, they also show a high level of gene expression.
Thus, Polytene chromosomes are massive chromosomes that are commonly found in insect salivary glands They are formed when chromosomes are duplicated repeatedly without being separated.

Note:
At interphase, polytene chromosomes have distinct thick and thin banding patterns. Originally, these patterns were used to help map chromosomes, identify small chromosome mutations, and identify taxonomic groups. They are now being used to investigate the role of genes in transcription.