Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

7. DNA and Chromosome Structure

Eukaryotic Chromosome Structure

Genetics

7. DNA and Chromosome Structure

Eukaryotic Chromosome Structure

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2:08 minutes

Problem 5

Textbook Question

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

Verified step by step guidance

Understand that polytene chromosomes are large, specialized chromosomes found in certain tissues of organisms like Drosophila. They are formed by repeated rounds of DNA replication without cell division, resulting in many sister chromatids aligned in parallel.

Recognize that a 'puff' in a polytene chromosome represents a region of chromatin decondensation. This decondensation indicates active transcription, where RNA polymerase is synthesizing RNA from the DNA template.

Experimentally, this process is confirmed by using radioactive uridine (a precursor for RNA synthesis). When cells are exposed to radioactive uridine, it gets incorporated into newly synthesized RNA, and the puff regions show high levels of radioactivity, indicating active transcription.

Another experimental method involves staining the chromosomes with dyes or antibodies specific to RNA polymerase or transcription factors. These stains localize to the puff regions, further confirming transcriptional activity.

Finally, researchers can use modern techniques like fluorescence in situ hybridization (FISH) to detect specific RNA transcripts in the puff regions, providing direct evidence of gene expression occurring at these sites.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Polytene Chromosomes

Polytene chromosomes are oversized chromosomes that result from multiple rounds of DNA replication without cell division, leading to many identical sister chromatids aligned 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.

Puffs in Polytene Chromosomes

Puffs are localized swellings on polytene chromosomes that indicate regions of active transcription. They represent areas where genes are being expressed, as the chromatin becomes more relaxed and accessible to the transcription machinery. The presence of puffs can be visualized under a microscope, providing insight into gene activity in response to developmental cues or environmental stimuli.

Experimental Evidence of Gene Expression

Experimental techniques such as in situ hybridization and RNA sequencing can be used to demonstrate gene expression in polytene chromosomes. In situ hybridization allows researchers to visualize specific RNA transcripts in the puffs, confirming that these regions are actively transcribing genes. Additionally, changes in puffing patterns in response to various stimuli can be monitored, providing further evidence of the dynamic nature of gene expression.

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