Fundamental Biology & Genetics

Fundamental biology and human physiology form the baseline of medical and agricultural technologies. This guide covers cellular mechanics, genetics, human body systems, biochemistry, systematics, evolution, and developmental biology.

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1. Cell Biology & Tissues

Cell Theory, Prokaryotes & Eukaryotes

Cue Words	Notes
What is Cell Theory, who proposed it, and what are its key tenets?	Cell Theory: Proposed by Schleiden and Schwann. Key Tenets: States that all living organisms are composed of cells, and cells are the basic structural and functional units of life.
Compare the structural differences between prokaryotic and eukaryotic cells.	Prokaryotic Cells (Archaea, Bacteria): No membrane-bound nucleus (DNA is in a nucleoid region); single circular chromosome + plasmids; small ribosomes (70S); lack membrane-bound organelles (like mitochondria); reproduce rapidly. Eukaryotic Cells (Protists, Fungi, Plants, Animals): Defined nucleus with nuclear envelope; multiple linear chromosomes; large ribosomes (80S); contain complex membrane-bound organelles.
What are the key exceptions to the Cell Theory?	Viruses: Acellular entities that are inert outside host cells. Mature Mammalian Red Blood Cells (RBCs): Lack a nucleus and mitochondria to maximize space for oxygen-carrying hemoglobin.

Cell Organelles & Structures

Cue Words	Notes
Describe the function of the cell nucleus and the role of the nucleolus.	Nucleus: The control center of the cell housing DNA. Nucleolus: Located inside the nucleus; responsible for ribosomal RNA (rRNA) synthesis.
Explain the function and unique genetic features of Mitochondria and Chloroplasts.	Mitochondria: Powerhouse of the cell; site of aerobic respiration and ATP synthesis. Possess their own circular maternal DNA (mtDNA) and 70S ribosomes (evidence of Endosymbiotic Theory). Chloroplasts: Found in plants/algae; contain chlorophyll for photosynthesis. Like mitochondria, they possess autonomous circular DNA.
What is a Nitroplast and its significance?	Nitroplast: A recently discovered nitrogen-fixing organelle in the marine algae Braarudosphaera bigelowii. Significance: Challenges the long-held scientific consensus that only bacteria are capable of nitrogen fixation.
Detail the roles of Lysosomes, Ribosomes, and the Hayflick Limit.	Lysosomes: Contain hydrolytic enzymes for intracellular digestion ("suicide bags"). Ribosomes: Sites of protein translation (composed of rRNA and proteins). Hayflick Limit: The finite number of times a normal human somatic cell population can divide (typically 40–60 times) before cell division stops due to telomere shortening.

Chromosome Structure & Cell Cycle Regulation

Cue Words	Notes
Classify chromosomes based on centromere position.	Metacentric: Centromere in the middle; forms V-shape during anaphase. Submetacentric: Centromere slightly off-center; forms L-shape. Acrocentric: Centromere near the end; forms J-shape. Telocentric: Centromere at the terminal end; forms I-shape (not present in humans).
Contrast Euchromatin and Heterochromatin, and list examples of Giant Chromosomes.	Euchromatin: Loosely packed, active transcription, stains light. Heterochromatin: Densely packed, inactive/silenced transcription, stains dark. Giant Chromosomes: Polytene (salivary glands of dipteran flies; repeated replication without division) and Lampbrush (oocytes of amphibians; highly active in transcription).
Explain the regulation checkpoints of the cell cycle and the role of tumor suppressors.	Phases: $G_1$ (growth), $S$ (DNA replication), $G_2$ (mitotic preparation), and $M$ (mitosis/cell division). Checkpoints: Controlled by Cyclins and Cyclin-Dependent Kinases (CDKs). Tumor Suppressors: Proteins like p53 (triggers DNA repair or apoptosis if damage is irreparable) and Rb (Retinoblastoma) act as brakes at the $G_1/S$ checkpoint. Mutation/loss of these proteins leads to cancer.

Mitosis vs Meiosis

Cue Words	Notes
Compare Mitosis and Meiosis: cell types, division phases, and daughter cell ploidy.	Mitosis (Equational Division): Occurs in somatic cells for growth and repair. One diploid parent cell ($2n$) divides into two identical diploid daughter cells ($2n$). Meiosis (Reductional Division): Occurs in germline cells during gametogenesis. One diploid parent cell ($2n$) divides twice to produce four non-identical haploid gametes ($n$).
How is genetic recombination achieved during meiosis?	Genetic Recombination: Occurs during Prophase I of Meiosis via Crossing Over (exchange of genetic material between homologous chromosomes at Chiasmata), ensuring genetic diversity.

Plant & Animal Tissues

Cue Words	Notes
Detail plant meristematic and simple permanent tissues: functions and properties.	Meristematic Tissues: Actively dividing cells (apical, lateral, intercalary). Simple Permanent Tissues: Parenchyma: Thin-walled, living cells; function in photosynthesis, storage, and secretion. Collenchyma: Living cells with unevenly thickened cellulose walls; provide mechanical support and flexibility to growing stems. Sclerenchyma: Dead cells with thick, lignified walls; provide mechanical rigidity (e.g., coconut husk, plant fibers).
Compare Xylem and Phloem vascular transport in plants.	Xylem: Transports water and minerals unidirectionally from roots to leaves. Consists of tracheids, vessels, xylem parenchyma (living), and xylem fibers. Phloem: Transports organic food (photosynthates) bidirectionally from leaves to storage organs. Consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibers (dead).
Name the four major types of animal tissues and their primary functions.	Epithelial: Protective covering, lining, and glandular secretion (e.g., skin, lining of gut). Connective: Binds, protects, and supports organs (e.g., blood, bone, cartilage, adipose). Muscular: Responsible for movement (Skeletal: striated/voluntary; Smooth: non-striated/involuntary; Cardiac: striated/involuntary). Nervous: Specialized for electrical signal transmission (Neurons and Glial cells).

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2. Molecular Biology & Genetics

Nucleic Acid Topology & Gene Structure

Cue Words	Notes
Explain DNA supercoiling, the role of Topoisomerases, and alternative DNA structures.	DNA Supercoiling: Twisting of the double helix to fit inside the cell. Managed by Topoisomerases (which cut and rejoin DNA to relieve torsional strain during replication). Alternative DNA Structures: B-DNA: Standard right-handed helix (wet physiological conditions). A-DNA: Dehydrated right-handed helix; wider and flatter. Z-DNA: Left-handed zigzag double helix; associated with active transcription. G-Quadruplex: Four-stranded DNA structures rich in Guanine; found in promoters and telomeres, linked to gene regulation.
Identify the main structural and regulatory components of a gene.	Exons: Coding sequences expressed in proteins. Introns: Non-coding sequences spliced out during RNA processing. Regulatory Elements: Promoters (RNA polymerase binding site), Enhancers (bind activators to boost transcription), and Silencers (bind repressors). Transcription Units: Monocistronic (one gene per mRNA; eukaryotes) and Polycistronic (multiple genes under one promoter; prokaryotic operons).

The Genetic Code & Translation

Cue Words	Notes
Detail the Central Dogma, transcription, and post-transcriptional modifications in eukaryotes.	Central Dogma: Flow of genetic information: DNA $\rightarrow$ RNA $\rightarrow$ Protein. Transcription: Regulated by RNA Polymerase to synthesize RNA from a DNA template. Post-Transcriptional Modifications: 5' Capping, 3' Polyadenylation (Poly-A tail), and Splicing (removing introns). Alternative splicing allows one gene to code for multiple proteins.
What are the primary properties of the genetic code?	Triplet Codon: 3 nucleotides code for 1 amino acid. Degenerate: Multiple codons can code for the same amino acid (64 codons for 20 amino acids). Wobble Hypothesis: The third base of a codon can tolerate non-standard pairing with tRNA, reducing the number of required tRNAs.

Mendelian Genetics & Extensions

Cue Words	Notes
List and explain Gregor Mendel's three laws of inheritance.	Law of Dominance: In a heterozygote, one allele masks the phenotypic expression of another allele at the same locus. Law of Segregation: Allele pairs separate during gamete formation, so each gamete carries only one allele for each gene. Law of Independent Assortment: Alleles of two or more different genes sort into gametes independently of one another.
What are Codominance, Incomplete Dominance, and Linkage? Give examples.	Codominance: Both alleles are fully expressed in the heterozygote (e.g., AB Blood Group, where both $I^A$ and $I^B$ alleles are dominant over $i$, but co-dominant with each other). Incomplete Dominance: Neither allele is completely dominant, resulting in a blended intermediate phenotype (e.g., pink snapdragons from red and white parents). Linkage and Crossing Over: Genes located close together on the same chromosome tend to be inherited together, violating the Law of Independent Assortment. Recombination maps estimate genetic distances.
How do pedigree inheritance types differ, and why do sex-linked traits affect males more frequently?	Pedigree & Inheritance Types: Autosomal dominant/recessive, and Sex-linked. Sex-linked Traits: Mostly X-linked recessive like Haemophilia or Color Blindness. They affect males much more frequently as they possess only one X chromosome (hemizygous), meaning a single recessive allele triggers the condition.

Mutations & DNA Repair

Cue Words	Notes
Compare point mutations, frameshift mutations, and chromosomal aberrations.	Point Mutation: Substitution of a single nucleotide (e.g., transition, transversion). Can cause missense, nonsense (creates a stop codon), or silent mutations. Frameshift Mutation: Insertion or deletion of nucleotides not in multiples of three, shifting the reading frame. Chromosomal Aberrations: Deletions, duplications, inversions (reversing direction), and translocations (exchanging segments between non-homologous chromosomes).
Identify common mutagens and DNA repair pathways.	Mutagens: Physical (UV light, X-rays), chemical (alkylating agents), or biological (viruses). DNA Repair: Mismatch repair, Base Excision Repair (BER), and Nucleotide Excision Repair (NER).

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3. Human Physiology & Body Systems

Blood & Circulation

Cue Words	Notes
Detail blood composition: plasma, RBCs, WBCs, and platelets.	Blood Composition: Plasma (~55%): Liquid matrix containing water, proteins (albumin, globulin, fibrinogen), electrolytes, and hormones. Red Blood Cells (RBCs - Erythrocytes, ~45%): Biconcave, lack nucleus/mitochondria; packed with Hemoglobin (iron-containing protein) for oxygen transport. Lifespan ~120 days. White Blood Cells (WBCs - Leucocytes, <1%): Immune defense cells (granulocytes, lymphocytes, monocytes). Platelets (Thrombocytes, <1%): Cellular fragments crucial for blood clotting.
Explain ABO/Rh blood grouping, universal donors/recipients, and Erythroblastosis Fetalis.	Universal Donor: O negative (O-) (lacks A, B, and Rh antigens on RBCs). Universal Recipient: AB positive (AB+) (lacks anti-A, anti-B, and anti-Rh antibodies in plasma). Erythroblastosis Fetalis: Hemolytic disease of the newborn caused by Rh incompatibility (Rh-negative mother carrying an Rh-positive fetus).
Compare heart structures and circulation types across fish, amphibians, reptiles, birds, and mammals.	Comparative Heart Anatomy: 2-Chambered Heart (1 Atrium, 1 Ventricle): Fish; single circulation (heart $\rightarrow$ gills $\rightarrow$ body $\rightarrow$ heart). 3-Chambered Heart (2 Atria, 1 Ventricle): Amphibians and reptiles (except crocodiles); incomplete double circulation. 4-Chambered Heart (2 Atria, 2 Ventricles): Birds, mammals, and crocodiles; complete double circulation (prevents mixing of oxygenated and deoxygenated blood).

Digestive System & Gut Microbiome

Cue Words	Notes
Identify key enzymes and digestive fluids in the mouth, stomach, liver, pancreas, and small intestine.	Human Digestive Tract & Key Enzymes: Salivary Glands: Salivary amylase (breaks down starch into maltose). Stomach: Secretes HCl (activates pepsin) and Pepsin (digests proteins into peptones). Liver: Secretes Bile (stored in gallbladder; emulsifies fats; contains no enzymes). Responsible for detoxification and glycogen storage. Pancreas (Exocrine): Secretes Trypsin (proteins), Lipase (fats), and Amylase (carbohydrates) into the duodenum. Small Intestine: Final site of chemical digestion and nutrient absorption via villi/microvilli.
Explain the gut microbiome: location, scale, and physiological roles.	Gut Microbiome: Trillions of microbes residing in the large intestine (weighing up to 2 kg). Physiological Roles: Regulates digestion, synthesizes vitamins (Vitamin K and some B-vitamins), and shapes immune health.

Respiration & Excretion

Cue Words	Notes
Compare aerobic and anaerobic respiration: oxygen requirements, ATP yield, and end products.	Aerobic Respiration: Requires Oxygen; yields 36–38 ATP per glucose molecule, converting it to $CO_2$ and $H_2O$. Anaerobic Respiration: Occurs without Oxygen; yields only 2 ATP. Converts glucose to Lactic Acid (in animal muscles during strenuous exercise) or Ethanol and $CO_2$ (in yeast fermentation).
How are gases transported in blood, and what is the Bohr Effect?	Gas Transport: Hemoglobin binds reversibly with oxygen to form Oxyhemoglobin. Bohr Effect: Increased carbon dioxide concentration (low pH) in tissues decreases hemoglobin's affinity for oxygen, promoting oxygen release where needed.
Define the three modes of excretion based on nitrogenous waste, and detail nephron function.	Excretion Modes: Ammonotelism: Excretes highly toxic Ammonia; requires vast water volumes (e.g., aquatic fish). Ureotelism: Excretes less toxic Urea; requires moderate water (e.g., mammals, amphibians). Uricotelism: Excretes non-toxic, insoluble Uric Acid as a paste; requires minimal water (e.g., birds, reptiles, insects). Nephron Function: The functional unit of the kidney. Performs Ultrafiltration in the Bowman's capsule/Glomerulus, Selective Reabsorption in the Loop of Henle and proximal tubules, and Tubular Secretion in distal tubules to form urine.

Endocrine & Nervous Systems

Cue Words	Notes
List the major endocrine glands and the specific hormones they secrete.	Endocrine Glands & Major Hormones: Pituitary (Master Gland): Under control of the Hypothalamus; secretes Growth Hormone (GH), Thyroid-Stimulating Hormone (TSH), FSH, LH, Oxytocin, and ADH (regulates water reabsorption). Thyroid: Secretes Thyroxine (regulates basal metabolic rate; contains iodine). Parathyroid: Secretes PTH (raises blood calcium levels). Adrenal Gland: Cortex secretes Cortisol and Aldosterone; Medulla secretes Adrenaline (epinephrine) and Noradrenaline (fight-or-flight response). Pancreas (Endocrine): Beta cells secrete Insulin (lowers blood glucose); Alpha cells secrete Glucagon (raises glucose). Pineal Gland: Secretes Melatonin (regulates circadian rhythm).
Explain the organization of the nervous system and the functions of key brain structures.	Nervous System Organization: CNS (Brain and Spinal Cord) and PNS (Cranial and spinal nerves). ANS (Autonomic) is split into Sympathetic (fight-or-flight) and Parasympathetic (rest-and-digest). Brain Structures: Cerebrum: Thought, sensory integration. Cerebellum: Motor control, balance. Medulla Oblongata: Involuntary respiration, heart rate. Hypothalamus: Temperature, hunger, endocrine link.
Describe synaptic transmission in neurons.	Synaptic Transmission: Dendrites receive signals $\rightarrow$ Cell Body $\rightarrow$ Axon. At the synapse, electrical signals are converted to chemical Neurotransmitters (e.g., Acetylcholine, Dopamine, Serotonin, GABA) to cross the synaptic cleft.

Musculoskeletal & Reproductive Systems

Cue Words	Notes
Detail the musculoskeletal system: bone count, joint types, and muscle types.	Bones: 206 in adults (infants have ~300 which fuse over time). Femur is the longest bone; Stapes (ear) is the smallest. Joints: Fibrous (immovable, e.g., skull sutures), Cartilaginous (limited movement, e.g., vertebrae), and Synovial (freely movable, e.g., ball-and-socket shoulder, hinge knee). Muscle Types: Skeletal (voluntary), Smooth (involuntary), Cardiac (involuntary).
Explain human reproduction: sites of gamete production, fertilization, implantation, and the menstrual cycle phases.	Reproductive Organs: Testes produce sperm (via spermatogenesis) and testosterone. Ovaries produce ova and estrogen/progesterone. Fertilization occurs in the Fallopian tubes; implantation occurs in the Uterus. Menstrual Cycle (28-day average): Follicular Phase: FSH stimulates follicle growth; estrogen builds uterine lining. Ovulation (Day 14): Triggered by a sharp surge in Luteinizing Hormone (LH), releasing the egg. Luteal Phase: Ruptured follicle becomes the Corpus Luteum, secreting progesterone to maintain the uterine lining. If fertilization fails, corpus luteum degenerates, leading to menstruation.

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4. Biochemistry & Metabolism

Biomolecules & Bioenergetics

Cue Words	Notes
Compare the structure and properties of carbohydrates, proteins, and lipids.	Biomolecules: Carbohydrates: Monosaccharides (glucose, fructose), Disaccharides (sucrose, lactose), and Polysaccharides (starch, glycogen, cellulose). Proteins: Polymers of amino acids linked by peptide bonds. Structure hierarchies: Primary (linear sequence), Secondary (alpha-helix, beta-pleated sheet), Tertiary (overall 3D conformation of single chain), Quaternary (arrangement of multiple subunits like Hemoglobin). Fats & Lipids: Triglycerides composed of glycerol and fatty acids. Essential for cell membranes (phospholipid bilayer).
Identify the energy currency and intracellular second messenger of the cell.	Energy Currency: **ATP (Adenosine Triphosphate)**. Second Messenger: **Cyclic AMP (cAMP)** acts as a vital intracellular second messenger in hormone signal transduction.

Metabolic Pathways & Enzymes

Cue Words	Notes
Detail glycolysis, the Krebs cycle, and the Electron Transport Chain.	Core Pathways: Glycolysis (Cytoplasm): Anaerobic breakdown of Glucose into Pyruvate; yields 2 net ATP. Krebs / TCA Cycle (Mitochondrial Matrix): Aerobic cycle converting acetyl-CoA into $CO_2$, generating NADH, $FADH_2$, and ATP. Electron Transport Chain (Inner Mitochondrial Membrane): Oxidative phosphorylation. Protons pumped across the membrane create a gradient; their flow back through ATP Synthase drives massive ATP synthesis (Chemiosmotic Theory).
Explain enzyme kinetics and the differences between competitive and non-competitive inhibition.	Michaelis-Menten Kinetics: Describes the rate of enzymatic reactions relative to substrate concentration ($K_m$ is the substrate concentration at half-maximum velocity $V_{max}$). Enzyme Inhibition & Regulation: Competitive: Competitor binds active site; increases $K_m$, $V_{max}$ unchanged. Non-competitive: Binds allosteric site; reduces $V_{max}$, $K_m$ unchanged. Allosteric Regulation: Activity altered by effector binding at a site separate from the active site.

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5. Systematics & Kingdoms of Life

Nomenclature & Whittaker's 5 Kingdoms

Cue Words	Notes
What is binomial nomenclature, and what are the different types of taxonomic specimens?	Binomial Nomenclature: System introduced by Carl Linnaeus; every species is named with a Genus and Species name. Regulated by the ICZN (International Code of Zoological Nomenclature). Type Specimens: Holotype (the single specimen used to describe a new species), Lectotype, Neotype (replacement specimen if holotype is lost), Syntype.
Detail R.H. Whittaker's Five Kingdoms classification.	R.H. Whittaker's Five Kingdoms (1969): Monera: Prokaryotic, unicellular (e.g., Bacteria, Blue-green algae). Protista: Eukaryotic, unicellular (e.g., Amoeba, Paramecium). Fungi: Eukaryotic, heterotrophic, multicellular (except yeast), cell walls containing Chitin (e.g., mushrooms, bread mold). Plantae: Eukaryotic, multicellular, autotrophic (cellulose cell walls). Animalia: Eukaryotic, multicellular, heterotrophic (lack cell walls).

Plant & Animal Kingdoms Deep Dive

Cue Words	Notes
Classify the five divisions of the plant kingdom with characteristics and examples.	Plant Kingdom Divisions: Thallophytes (Algae): Simplest plants; body is undifferentiated (thallus) (e.g., Spirogyra). Bryophytes: "Amphibians of the plant kingdom"; lack vascular tissue; require water for sexual reproduction (e.g., Mosses). Pteridophytes: First terrestrial plants to develop vascular tissues (Xylem/Phloem) (e.g., Ferns). Gymnosperms: Seed-producing plants; seeds are "naked" (not enclosed in an ovary/fruit) (e.g., Pinus, Cycas). Angiosperms: Flowering plants; seeds are enclosed inside fruits. Divided into Monocots and Dicots.
Outline the key divisions of invertebrates and vertebrates in the animal kingdom.	Invertebrates (Non-Chordates): Porifera (sponges), Cnidaria (corals/jellyfish), Platyhelminthes (flatworms), Nematoda (roundworms), Annelida (segmented worms), Arthropoda (largest phylum; jointed appendages, chitinous exoskeleton, e.g., insects, spiders), Mollusca (soft-bodied, calcium shells, e.g., snails), Echinodermata (spiny-skinned, radial symmetry, e.g., starfish). Vertebrates (Chordates): Pisces (fish), Amphibia (frogs), Reptilia (snakes, crocodiles), Aves (birds), Mammalia (mammals).

Biological Adaptations

Cue Words	Notes
Compare Hibernation and Aestivation, and explain diadromous fish migrations.	Hibernation: "Winter sleep"; reduced metabolic activity during extreme cold (e.g., polar bears, bats). Aestivation: "Summer sleep"; dormancy to survive extreme heat and drought (e.g., lungfish, land snails). Diadromous Fish Migrations: Anadromous: Migrate from saltwater to freshwater to breed (e.g., Salmon). Catadromous: Migrate from freshwater to saltwater to breed (e.g., Freshwater Eel).

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6. Origin of Life & Evolution

Theories of Origin & Evolutionary Mechanisms

Cue Words	Notes
What are the primary hypotheses and experiments explaining the origin of life?	Origin of Life Theories: Primordial Soup Hypothesis (Oparin-Haldane): Life arose from simple organic molecules formed in a reducing atmosphere. Miller-Urey Experiment (1953): Simulated early Earth conditions, proving amino acids could synthesize abioticly. RNA World Hypothesis: Proposes that self-replicating RNA was the precursor to modern DNA/protein-based life.
Contrast Darwinian Natural Selection, Hugo de Vries' Mutation Theory, and the Modern Synthetic Theory of evolution.	Darwinian Natural Selection: "Survival of the fittest"; environmental pressure selects beneficial variations. Mutation Theory (Hugo de Vries): Evolution occurs via sudden, large mutations (saltation) rather than gradual variations. Modern Synthetic Theory: Merges Darwin's selection with Mendelian genetics and population dynamics.
Distinguish between divergent and convergent evolution with examples.	Divergent Evolution: Related species evolve different traits due to different environments (adaptive radiation, e.g., Darwin's finches). Convergent Evolution: Unrelated species develop similar traits due to similar environmental pressures (e.g., wings of insects and birds).

Fossil Records & Population Genetics

Cue Words	Notes
Outline the fossil lineages of horse and human evolution.	Fossil Lineages: Horse Evolution: Well-documented morphological changes (size increase, reduction of toes, tooth crown changes) from Eohippus to Equus. Human Evolution: Lineage starting from Australopithecus $\rightarrow$ Homo habilis (first tool user) $\rightarrow$ Homo erectus (first to control fire) $\rightarrow$ Homo neanderthalensis $\rightarrow$ Homo sapiens.
State the Hardy-Weinberg Principle: assumptions and deviations.	Hardy-Weinberg Principle: States that allele and genotype frequencies in a population will remain constant in the absence of evolutionary influences. Assumptions: Random mating, large population size, no mutation, no gene flow (migration), and no natural selection. Deviations: Induced by Genetic Drift (random changes in small populations, e.g., Founder Effect, Bottleneck Effect) and Gene Flow.

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7. Developmental Biology

Gametogenesis, Fertilization & Embryogenesis

Cue Words	Notes
Compare Spermatogenesis and Oogenesis: continuity, timing, and cells produced.	Gametogenesis: Spermatogenesis: Continuous production of four functional haploid sperm from one diploid spermatogonium. Oogenesis: Discontinuous production of one functional haploid egg and three polar bodies. Suspended at Prophase I at birth, resumes at puberty, and suspends again at Metaphase II until fertilization.
Explain Capacitation, Gastrulation, and Hox genes in development.	Capacitation: The physiological changes a sperm undergoes in the female reproductive tract to gain the ability to fertilize the egg. Gastrulation: Rearrangement of the blastocyst into three primary germ layers (endoderm, mesoderm, ectoderm). Hox Genes: Highly conserved master regulator genes that determine the body plan and structural axes development of embryos.
Define Teratogenesis and its impact on embryonic development.	Teratogenesis: Congenital malformations caused by environmental agents (drugs, radiation) during embryonic development (e.g., Thalidomide disaster).

:::- Cell is the basic structural and functional unit of life, characterized by a cell membrane, cytoplasm, and genetic material (DNA/RNA). - R.H. Whittaker proposed the Five Kingdom classification: Monera, Protista, Fungi, Plantae, Animalia. - Eukaryotic cells have a membrane-bound nucleus and organelles; prokaryotic cells (bacteria, archaea) lack these. - The cell membrane follows the fluid mosaic model (phospholipid bilayer + proteins) and is selectively permeable. - Mitochondria, the "powerhouse of the cell" (site of ATP formation), are double membrane-bound and carry their own circular DNA. - Chloroplasts occur only in plant cells, contain chlorophyll, are the site of photosynthesis, and have small circular DNA. - The endosymbiotic theory proposes that mitochondria and chloroplasts evolved from prokaryotic organisms engulfed by ancestral eukaryotic cells. - "Nitroplast," a newly identified nitrogen-fixing organelle, was discovered in the marine alga Braarudosphaera bigelowii. - Humans have 46 chromosomes (23 pairs); diploid cells (2n) carry paired chromosomes while haploid cells (n) carry a single set. - Meiosis (reduction division for gamete formation) produces four haploid cells and involves crossing over. - The Hayflick limit is the maximum number of times a normal cell population can divide, determined by telomere length. - Mitochondrial DNA is inherited only from the mother; defective maternal mitochondria cause diseases like Leigh's disease. - Mitochondrial replacement techniques (pronuclear transfer, maternal spindle transfer) produce a child with DNA from three parents. - Genome is the complete genetic material of an organism; a gene is the functional unit of inheritance that codes for a protein. - DNA is a double helix of deoxyribose-phosphate backbone with nitrogenous bases (purines: adenine, guanine; pyrimidines: cytosine, thymine). - RNA is single-stranded, uses ribose sugar and uracil (instead of thymine), and is less stable but more catalytically active than DNA. - The 2024 Nobel Prize in Physiology or Medicine was awarded to Victor Ambros and Gary Ruvkun for discovering microRNA-based gene regulation. - MicroRNA does not code for protein but regulates gene expression by blocking translation of target mRNA. - The genetic code has 64 codons: 61 code for amino acids and 3 are stop codons; it is universal and degenerate. - Har Gobind Khorana helped decipher the genetic code. - Sickle cell anemia is caused by a point mutation in the hemoglobin gene. - A Single Nucleotide Polymorphism (SNP) is a naturally occurring variation at a single DNA base position, used as a biomarker. - Types of DNA mutations include deletion, duplication, inversion, and point mutation. - Viruses are small obligate intracellular particles, visible only under an electron microscope, that infect and replicate using host cell machinery. - Viruses were first characterised via the Tobacco Mosaic Disease, which passed through bacterial filters and could not be cultured on artificial media, feeding into the germ theory of disease. - The viral capsid (protein coat) helps the virus enter the host cell, aids in assembly, and triggers the host immune response; capsid subunits (capsomeres) assemble from protein building blocks called protomeres. - By genome type: most DNA viruses are double-stranded DNA (dsDNA), most RNA viruses and plant viruses are single-stranded RNA (ssRNA), and most bacteriophages are dsDNA. - Viroids, discovered in 1971 by T.O. Diener, are smaller than viruses, consist of free RNA lacking a protein coat, and have low molecular weight. - Prions are infectious agents made of abnormally folded protein, roughly similar in size to viruses. - Innate immunity is non-specific, present from birth, and comprises physical (skin/mucus), physiological (stomach acid), and cellular (WBCs, B-cells, T-cells) barriers. - Acquired (adaptive) immunity is pathogen-specific, works on the principle of immunological memory, and comprises primary and secondary immune responses carried out by B-lymphocytes and T-lymphocytes. - CD4+ helper T-cells act as the immune system's 'command centre' while CD8+ cytotoxic T-cells directly kill infected cells. - A helper T-cell 'licenses' a B-cell via the CD40L signal, triggering the B-cell to produce antibodies that neutralise pathogens (the humoral response), while T-cells directly kill infected cells. - Autoimmunity occurs when the immune system cannot distinguish the body's own cells from pathogens and attacks self-cells, resulting in autoimmune diseases such as rheumatoid arthritis. - The Human Genome Project aimed to identify all ~20,000-25,000 human genes, sequence about 3.2 billion base pairs, store the data, improve analysis tools, transfer technology to industry, and address related ethical/legal/social issues. - Human Genome Project key findings: ~3.2 billion base pairs across 23 chromosome pairs; only 1-2% of DNA codes for protein; most non-coding DNA is functional, not 'junk'; humans have only ~20,000 genes; genome complexity arises from alternative splicing; humans are 99.9% genetically identical. - The Telomere-to-Telomere (T2T) Project sequenced heterochromatin regions not covered by the Human Genome Project (previously assumed to be junk DNA). - Heterochromatin is more condensed, gene-silenced (methylated), gene-poor (high AT content) and stains darker; euchromatin is less condensed, gene-expressing, gene-rich (high GC content) and stains lighter. - Tmesipteris oblanceolata, a fork fern species, has the largest known genome at 160 billion base pairs -- more than 50 times the size of the human genome. - Ovoid cells are a newly identified type of brain cell that play a fundamental role in recognition memory -- the brain's process of distinguishing new from familiar objects to form long-term memories. - Molecular motors are molecular machines within a cell that convert the chemical energy stored in ATP into mechanical work. - The mitogenome is a small, circular double-stranded DNA chromosome inside mitochondria, inherited only from the mother.