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
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
7. DNA and Chromosome Structure
DNA as the Genetic Material
5:49 minutes
Problem 1a
Textbook Question
What results from the experiments of Frederick Griffith provided the strongest support for his conclusion that a transformation factor is responsible for heredity?
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1
<span>Step 1: Understand the context of Frederick Griffith's experiments, which were conducted in 1928 to study the bacterium Streptococcus pneumoniae.</span>
<span>Step 2: Recognize the two strains of bacteria used in Griffith's experiments: the virulent S (smooth) strain, which has a polysaccharide capsule and causes disease, and the non-virulent R (rough) strain, which lacks the capsule and does not cause disease.</span>
<span>Step 3: Recall the key experiment where Griffith injected mice with a mixture of heat-killed S strain bacteria and live R strain bacteria. The mice developed pneumonia and died, and live S strain bacteria were recovered from the dead mice.</span>
<span>Step 4: Analyze the results, which suggested that some 'transforming factor' from the heat-killed S strain bacteria was taken up by the live R strain bacteria, transforming them into the virulent S strain.</span>
<span>Step 5: Conclude that the strongest support for Griffith's conclusion was the recovery of live S strain bacteria from the mice injected with the mixture, indicating that the transformation factor was responsible for transferring hereditary information.</span>
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Griffith's Experiment
Frederick Griffith conducted experiments in 1928 using two strains of Streptococcus pneumoniae: a virulent strain (smooth) and a non-virulent strain (rough). He discovered that when he injected mice with heat-killed virulent bacteria mixed with live non-virulent bacteria, the mice developed pneumonia and died. This indicated that some 'transforming principle' from the dead bacteria had transformed the non-virulent strain into a virulent one.
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Transformation
Transformation is a process in which a bacterium takes up foreign DNA from its environment and incorporates it into its own genome. In Griffith's experiment, the non-virulent bacteria acquired the genetic material from the heat-killed virulent bacteria, leading to the expression of virulence. This concept laid the groundwork for understanding how genetic information can be transferred between organisms.
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Transformation
Avery-MacLeod-McCarty Experiment
Building on Griffith's findings, the Avery-MacLeod-McCarty experiment in 1944 identified DNA as the 'transforming factor.' They demonstrated that only DNA from the heat-killed virulent bacteria could transform the non-virulent strain, providing strong evidence that DNA is the molecule responsible for heredity. This experiment confirmed Griffith's initial observations and established DNA as the genetic material.
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