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

Verified step by step guidance

1. Understand that polytene chromosomes are large chromosomes which have thousands of DNA strands. They are found in the salivary glands of Drosophila (fruit flies) and are used to study gene expression.
2. Recognize that a 'puff' in a polytene chromosome is a region where the chromatin has decondensed, indicating active transcription. This is where RNA synthesis is occurring.
3. Experimentally, the presence of a puff can be detected by autoradiography, where radioactive uridine is incorporated into newly synthesized RNA, highlighting areas of active transcription.
4. Another experimental method involves using in situ hybridization to detect specific RNA sequences, confirming that transcription is occurring in the puffed region.
5. Understand that the size and number of puffs can change in response to environmental factors, hormones, or developmental stages, providing insights into gene regulation.

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.