Mendel's Laws:
  Law of Dominance: In a heterozygote, dominant allele expresses
  Law of Segregation: Allele pairs separate during gamete formation
  Law of Independent Assortment: Genes on different chromosomes assort independently

Monohybrid cross (Tt × Tt):
  Genotype ratio: 1TT : 2Tt : 1tt = 1:2:1
  Phenotype ratio: 3 Tall : 1 short = 3:1

Dihybrid cross (TtRr × TtRr):
  Phenotype ratio: 9:3:3:1

Exceptions to Mendel's laws:
  Incomplete dominance: pink snapdragon (RR red × rr white → Rr pink)
  Co-dominance: AB blood group (both A and B antigens expressed)
  Multiple alleles: ABO blood group (Iᴬ, Iᴮ, i alleles)
  Linkage: genes on same chromosome tend to be inherited together

Blood Groups (must know for NEET):
  Group A: Iᴬ Iᴬ or Iᴬ i → A antigen, anti-B antibody
  Group B: Iᴮ Iᴮ or Iᴮ i → B antigen, anti-A antibody
  Group AB: Iᴬ Iᴮ → A and B antigens, no antibodies (Universal recipient)
  Group O: ii → No antigens, anti-A and anti-B antibodies (Universal donor for RBCs)
  Rh factor: +ve = Rh antigen present (D antigen); -ve = absent

DNA Structure (Watson-Crick model, 1953):
  Double helix, antiparallel strands
  Purines: Adenine, Guanine (2 rings)
  Pyrimidines: Cytosine, Thymine (1 ring)
  Base pairing: A=T (2 H-bonds), G≡C (3 H-bonds)
  Chargaff's rule: %A = %T, %G = %C
  1 turn = 10 base pairs = 3.4 nm

DNA Replication:
  Semi-conservative (Meselson-Stahl experiment proved)
  Origin → Helicase unwinds → Primase adds RNA primer
  DNA Pol III → synthesizes new strand 5' to 3'
  Leading strand: continuous synthesis
  Lagging strand: Okazaki fragments, joined by DNA Ligase
  DNA Pol I: removes RNA primer, fills gap

Transcription:
  DNA → mRNA (in nucleus)
  RNA Polymerase unwinds and copies template strand
  mRNA: 5'-AUG...codons...stop-3'

Translation:
  mRNA + ribosomes + tRNA → protein
  Codons: 3 bases = 1 amino acid
  AUG = start codon (Met)
  UAA, UAG, UGA = stop codons
  64 codons (61 amino acids + 3 stop) for 20 amino acids
  Genetic code is degenerate (multiple codons per aa) and universal

Ecological Levels: Organism → Population → Community → Ecosystem → Biosphere

Population interactions:
  Mutualism (+/+): both benefit (lichens, mycorrhizae, pollination)
  Commensalism (+/0): one benefits, other neutral (orchids on trees)
  Parasitism (+/-): parasite benefits, host harmed (Plasmodium, Ascaris)
  Predation (+/-): predator benefits, prey harmed
  Competition (-/-): both harmed (interspecific competition → competitive exclusion)
  Amensalism (0/-): one harmed, other neutral

Ecological pyramids:
  Pyramid of numbers: may be inverted (parasitic food chain)
  Pyramid of biomass: may be inverted (ocean: phytoplankton > zooplankton by numbers)
  Pyramid of energy: ALWAYS upright (10% law — only 10% energy passes to next level)

Biogeochemical cycles:
  Carbon cycle: photosynthesis ↔ respiration + combustion + decomposition
  Nitrogen cycle: N₂ → (N₂ fixation) → NH₃ → (nitrification) → NO₂ → NO₃
                  → (assimilation) → org N → (denitrification) → N₂
  Phosphorus cycle: no gaseous phase (rocks → soil → organisms → decomposers → soil)