Prolonged Prophase in the Salivary Glands of Drosophila

The salivary glands of Drosophila, commonly known as fruit flies, have been extensively studied in genetics and cytogenetics due to their large and easily observable chromosomes. During the developmental stages of the salivary glands, the chromosomes undergo a unique process called polytenization, leading to the formation of polytene chromosomes. Polytene chromosomes are a distinct type of chromosomes characterized by their highly enlarged and elongated appearance.

Polytene Chromosomes
Polytene chromosomes are formed by repeated rounds of DNA replication without cell division. This results in the parallel alignment and fusion of sister chromatids, leading to the formation of a single giant chromosome. The DNA replication is not followed by the separation of sister chromatids, resulting in a structure with multiple identical strands of DNA called chromomeres. Polytene chromosomes are often observed in the salivary gland cells of Drosophila, where they play a crucial role in the regulation of gene expression.

Prolonged Prophase
Prophase is the first stage of mitosis or meiosis, characterized by the condensation of chromosomes and the breakdown of the nuclear envelope. In the salivary glands of Drosophila, the prophase stage is prolonged, allowing for the extensive replication and polytenization of the chromosomes. This prolonged prophase is unique to the salivary glands and is not observed in other cell types of Drosophila.

Role of Polytene Chromosomes
Polytene chromosomes in the salivary glands of Drosophila serve several important functions:
1. Increased DNA content: Polytene chromosomes allow for an increase in the amount of DNA in the cells, providing a higher gene dosage and facilitating the production of large amounts of RNA and protein.
2. Gene regulation: The polytene chromosome structure allows for the physical juxtaposition of homologous chromosomes, facilitating gene regulation and the coordination of gene expression.
3. Chromosome mapping: Polytene chromosomes provide a clear and visible representation of the genetic map, making them a valuable tool for genetic studies.

Conclusion
In conclusion, the chromosomes present in the prolonged prophase in the salivary glands of Drosophila are polytene chromosomes. These unique chromosomes are formed through repeated rounds of DNA replication without cell division, resulting in the parallel alignment and fusion of sister chromatids. Polytene chromosomes play a crucial role in gene regulation, chromosome mapping, and the increased DNA content in the salivary glands of Drosophila.

Polytene chromosome present in salivary gland of Droshophilla called as Gaint Chromosome having disc like structure k/a Ballbiani ring which is site of m-RNA formation.