Cytological bands
Polytene chromosomes Larval cells need a lot of RNA and protein to support rapid growth and development. These molecules are essential for building new tissues, organs, and cellular machinery quickly. Instead of dividing more often (which takes time and energy), some cells replicate their DNA without dividing to produce many copies of genes, so they can transcribe RNA and make protein much faster. Salivary glands are especially active because they produce large amounts of secretions, like glue proteins that help the larva attach to surfaces during pupation, and enzymes that may help with digestion of food. Some of these proteins and enzymes are secreted out into the larval environment or food, even though the larva also needs proteins and RNA for its own development. Secreting these proteins provides a functional advantage, for example, helping the larva anchor itself during pupation, aiding in digestion of food outside the body, or protecting against pathogens, which supports overall ...