What genetic process is occurring in a puff of a polytene chromosome? How do we know this experimentally?

Key Concepts

Polytene Chromosomes

Polytene chromosomes are oversized chromosomes that result from multiple rounds of DNA replication without cell division, leading to many identical sister chromatids lying side by side. They are commonly found in the salivary glands of certain insects, such as Drosophila, and are characterized by their distinct banding patterns, which reflect the organization of genes and regulatory elements.

Gene Puffing

Gene puffing refers to the localized swelling or expansion of polytene chromosomes, indicating active transcription of specific genes. This process is a visual representation of gene expression, where certain regions of the chromosome become more accessible to transcription machinery, allowing for the synthesis of RNA and subsequent protein production.

Experimental Evidence of Gene Activity

Experimental evidence for gene activity in polytene chromosomes can be obtained through techniques such as in situ hybridization, which uses labeled RNA probes to detect specific mRNA transcripts. Additionally, the use of inhibitors that block transcription can demonstrate the reversibility of puff formation, providing further insight into the dynamic nature of gene expression in these chromosomes.