Topics
Reproduction
Reproduction in Organisms
Sexual Reproduction in Flowering Plants
- Flower
- Accessory Organs
- Essential Parts of Flower: Androecium
- Essential Parts of Flower: Gynoecium
- Sexual Reproduction in Plants
- Pre-fertilization in Plant: Structure and Events
- Structure and Development of Anther
- Transverse Section of Mature Anther (Microsporangium)
- Microspores and Pollen Grains
- Advantages and Disadvantages of Pollen Grains
- Structure and Development of Ovule
- Artificial Hybridization or Artificial Fertilization
- Self-pollination
- Cross-pollination
- Abiotic Agents
- Biotic Agents
- Double Fertilization and Triple Fusion
- Post Fertilisation in Plant: Structures and Events
- Development of Seed
- Development of Fruit
Genetics and Evolution
Human Reproduction
- Microscopic Anatomy of Ovary
- Menstrual Cycle (Ovarian Cycle)
- Gametogenesis
- Embryo Development Upto Blastocyst Formation
- Fertilisation in Human
- Implantation in Human
Biology and Human Welfare
Reproductive Health
Biotechnology and Its Applications
Principles of Inheritance and Variation
- Introduction of Principles of Inheritance and Variation
- Terminology Related to Mendelism
- Mendel's Experiments on Inheritance
- Extensions of Mendelian Genetics (Deviation from Mendelism)
- Intragenic Interactions - Dominance
- Historical Development of Chromosome Theory
- Comparison Between Gene and Chromosome Behaviour
- Mendel's Laws > The Law of Segregation (Law of Purity of Gametes)
- Sex Determination in Some Insects
- Mendelian Genetics
- Chromosomal Disorders or Abnormalities
Ecology and Environment
Molecular Basis of Inheritance
Evolution
Human Health and Diseases
Strategies for Enhancement in Food Production
Microbes in Human Welfare
Biotechnology - Principles and Processes
Biotechnology and Its Application
- Concept of Biotechnology
- Transgenic Animals
- Biosafety Issues
Organisms and Populations
Ecosystem
Biodiversity and Its Conservation
- Biodiversity
- Importance of Species Diversity to the Ecosystem
- Patterns of Biodiversity
- Loss of Biodiversity
- Endangered Organisms
- Extinction
Environmental Issues
- Controlling Vehicular Air Pollution: a Case Study of Delhi
- Effects of Domestic Sewage and Industrial Effluents on Water
- Solid Wastes
- Radioactive Wastes
- Greenhouse Effect and Global Warming
- Ozone Depletion in the Stratosphere
- Degradation by Improper Resource Utilisation and Maintenance
- Radioactive Waste Management and E-waste
Estimated time: 2 minutes
CBSE: Class 12
Key Points: The Experimental Proof
- In 1958, Meselson and Stahl proved that DNA replicates semi-conservatively in E. coli.
- E. coli was first grown in heavy nitrogen (¹⁵N) medium, making all DNA heavy (¹⁵N-¹⁵N); cells were then transferred to normal nitrogen (¹⁴N) medium.
- DNA samples were separated using CsCl (caesium chloride) density gradient centrifugation to distinguish heavy, light and hybrid DNA.
- After one generation in ¹⁴N medium, DNA showed hybrid/intermediate density (¹⁵N-¹⁴N); after two generations, DNA was half hybrid + half light (¹⁴N-¹⁴N).
- In 1958, Taylor and colleagues also proved semi-conservative replication in Vicia faba (faba beans) using radioactive thymidine.
