Topics
Sexual Reproduction in Flowering Plants
- Flower
- Pre-fertilisation in Flowering Plant: Structures and Events
- Structure and Development of Anther
- Microsporogenesis
- Structure and Development of Male Gametophyte
- Pollen Viability and Storage
- Structure and Development of Ovule
- Megasporogenesis
- Development of Female Gametophyte or Embryo Sac
- Pollination
- Autogamy
- Geitonogamy
- Cross-pollination
- Agents of Pollination
- Anemophily
- Hydrophily
- Animal-Mediated Pollination (Zoophily)
- Outbreeding Devices
- Pollen Pistil Interaction
- Artificial Hybridization or Artificial Fertilization
- Double Fertilization and Triple Fusion
- Events in Sexual Reproduction > Post-Fertilization Structures and Events
- Endosperm
- Dicotyledonous Embryo
- Monocotyledonous Embryo
- The Seed
- Apomixis
- Polyembryony
Reproduction
Reproduction in Organisms
Human Reproduction
- Human Reproduction
- The Male Reproductive System
- The Female Reproductive System
- Gametogenesis
- Spermatogenesis
- Structure of Sperm
- Spermiogenesis
- Oogenesis
- Menstrual Cycle (Ovarian Cycle)
- Major Events of Menstrual Cycle
- Menstrual Hygiene
- Fertilization in Human
- Implantation in Human
- Pregnancy and Embryonic Development
- Parturition (Birth) in Human
- Lactation in Human
Genetics and Evolution
Reproductive Health
- Concept of Reproductive Health
- Population Explosion and Control Measures
- Birth Control
- Natural Contraceptive Methods
- Artificial Contraceptive Methods
- Induced Abortion or Medical Termination of Pregnancy (MTP)
- Sexually Transmitted Diseases (STD) or Sexually Transmitted Infections (STI)
- Infertility
- Assisted Reproductive Technology (ART)
- Amniocentesis
- Genetic Counselling
Biology and Human Welfare
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 Climate Change
- Ozone Depletion in the Stratosphere
- Degradation by Improper Resource Utilisation and Maintenance
- Radioactive Waste Management and E-waste
Principles of Inheritance and Variation
- Heredity and Variation
- Gregor Johann Mendel – Father of Genetics
- Mendel's Experiments on Inheritance
- Monohybrid Cross
- Punnett Square
- Back Cross and Test Cross
- Mendel's Laws > The Law of Dominance
- Mendel's Laws > The Law of Segregation (Law of Purity of Gametes)
- Exceptions to Mendel's Principles > Incomplete Dominance
- Exceptions to Mendel's Principles > Co-Dominance
- Dihybrid Cross
- Mendel's Laws > The Law of Independent Assortment
- Chromosomal Theory of Inheritance
- Linkage and Recombination
- Polygenic Inheritance
- Exceptions to Mendel's Principles > Pleiotropy
- Sex Determination
- Sex Determination in Humans
- Sex Determination in Honey Bees
- Mutations
- Pedigree Analysis
- Mendelian Disorders in Humans
- Chromosomal Disorders or Abnormalities
Biotechnology
Molecular Basis of Inheritance
- Deoxyribonucleic Acid (DNA)
- Structure of Polynucleotide Chain
- Packaging of DNA Helix
- Search for Genetic Material
- Griffith’s Experiment
- Avery, McCarty and MacLeod’s Experiment
- The Hershey-Chase Experiment
- Properties of Genetic Material
- The RNA World
- DNA Replication
- Conservative Replication
- Dispersive Replication
- Semi-Conservative Replication
- Meselson and Stahl’s Experiment
- Enzymes used in DNA Replication
- Mechanism of DNA Replication
- Protein Synthesis
- Reverse Transcription (Teminism)
- Transcription
- Transcription Unit and the Gene
- Process of Transcription in Bacteria
- Process of Transcription in Eukaryotes
- Genetic Code
- Characteristics of the Genetic Code
- Mutations and Genetic Code
- Transfer RNA (tRNA)
- Translation
- Regulation of Gene Expression
- The Lac Operon
- Human Genome Project
- DNA Fingerprinting
Ecology
Evolution
- Origin of Life on Earth
- Urey and Miller’s Experiment
- Evolution of Life Forms - a Theory
- Evidences Supporting the Theory of Evolution
- Adaptive Radiation
- Theories and Mechanism of Evolution
- Theories and Mechanism of Evolution
- Hardy Weinberg’s Principle
- Types of Selection
- Brief Account of Evolution
- Human Evolution
Human Health and Diseases
- Concept and Determinants of Health
- Modes of Transmission of Diseases through Pathogens
- Diseases Caused by Bacteria > Typhoid
- Diseases Caused by Bacteria > Pneumonia
- Diseases Caused by Viruses > Common Cold
- Diseases Caused by Protozoa > Malaria
- Diseases Caused by Protozoa > Amoebiasis (Amoeboic dysentery)
- Diseases Caused by Helminths > Ascariasis
- Diseases Caused by Helminths > Filariasis (Elephantiasis)
- Diseases Caused by Fungi > Ringworm
- Prevention and Control of Infectious Diseases
- Immunity
- Types of Immunity > Innate Immunity
- Types of Immunity > Acquired Immunity
- Vaccination and Immunization
- Allergies
- Autoimmunity
- The Immune System
- Acquired Immuno Deficiency Syndrome (AIDS)
- Cancer
- Causes of Cancer
- Symptoms and Diagnosis of Cancer
- Prevention/Treatment of Cancer
- Drugs and Alcohol Abuse
- Addiction and Dependence
- Effects of Drug and Alcohol Abuse
- Prevention and Control of Drugs and Alcohol Abuse
Strategies for Enhancement in Food Production
Microbes in Human Welfare
Biotechnology - Principles and Processes
Biotechnology and Its Application
Organisms and Populations
- Organisms and Their Environment
- Population and Population Attributes
- Population Growth
- Life History Variation
- Population Interactions
- Negative Interactions > Predation
- Negative Interactions > Competition
- Negative Interactions > Parasitism
- Positive Interactions > Commensalism
- Positive Interactions > Mutualism (Symbiosis)
Ecosystem
Biodiversity and Its Conservation
Estimated time: 12 minutes
CBSE: Class 12
CISCE: Class 12
CISCE: Class 12
The Problem: Nematode Infection
- Pathogen: Meloidogyne incognita (a root-knot nematode).
- Host Plant: Tobacco.
- Effect: The nematode invades plant roots and feeds on the cells, creating large galls or knots. This damages the crop and drastically reduces yield.
- Challenge: Because natural resistance to these nematodes does not naturally occur in most crops, biotechnology is required to protect them.
CBSE: Class 12
CISCE: Class 12
CISCE: Class 12
Basics of RNA Interference (RNAi)
RNAi is a natural method of cellular defence found in all eukaryotic organisms.
- Also Known As: Gene Silencing, Post-Transcriptional Gene Silencing (PTGS), or Quelling.
- Discovered By: Andrew Z. Fire and Craig C. Mello (initially discovered in C. elegans nematodes).
- Natural Triggers: In nature, RNAi is triggered by infections from viruses with RNA genomes or by mobile genetic elements (transposons) that replicate via an RNA intermediate.
Mechanism of Regulation: It limits gene transcription in two ways:
- Transcriptional Gene Silencing (TGS): Suppressing transcription directly.
- Post-Transcriptional Gene Silencing (PTGS): Degrading the RNA after it has been produced.
CBSE: Class 12
CISCE: Class 12
CISCE: Class 12
Bioengineering Resistance (The Process)
To protect the tobacco plant, scientists engineered it to trigger RNAi inside the attacking nematode, effectively blocking the expression of specific genes required for the nematode's survival.
- Gene Isolation: Identifying the target.
Specific disease-causing or essential genes are identified and isolated from the nematode (Meloidogyne incognita). - Gene Transfer (Transformation): Using Agrobacterium.
The isolated nematode gene is introduced into the tobacco plant's genome. This is done using Agrobacterium tumefaciens as a vector, which transfers a small segment of DNA into the plant genome through a process called transformation. - dsRNA Formation: Inside the host plant.
The introduced gene is designed to produce both sense and antisense mRNA inside the host plant. Because these two strands are complementary, they pair up to form double-stranded RNA (dsRNA). - Gene Silencing (RNAi): During nematode feeding.
When the nematode feeds on the transgenic plant's roots, it ingests this dsRNA. The dsRNA triggers the RNAi process, which binds to and prevents the translation of the corresponding, essential mRNA of the nematode. - Pest Elimination: The final result.
Because its specific mRNA is neutralised (silenced), the nematode cannot synthesise vital proteins. The parasite is unable to live in the transgenic host, and the tobacco plant is protected.
CISCE: Class 12
Key Points: Pest-Resistant Plants
- Nematode pests like Meloidogyne incognita damage plant roots, reduce crop yield, and require bioengineering for resistance.
- RNA interference (RNAi) is used to silence pest genes by preventing translation of nematode mRNA.
- In transgenic tobacco, both sense and antisense RNA are produced, forming dsRNA that triggers post-transcriptional gene silencing.
- Agrobacterium tumefaciens is used as a vector to transfer nematode-specific genes, making plants pest-resistant.
