NEET 2026 Complete Genetics & Evolution Notes – Last Minute Revision

🧬 NEET 2026 – Genetics & Evolution (Full Notes)

1. Heredity & Variation

Mendelian Inheritance

Parent Genotype → Law of Segregation (Alleles separate during gamete formation) → Gamete Formation (Each gamete carries one allele) → Fertilization (Random fusion of gametes) → F1 Generation

• Genotypic Ratio: 1:2:1
• Phenotypic Ratio: 3:1

Dihybrid Cross: Two traits, e.g., Seed shape × Seed color → Independent Assortment (Genes on different chromosomes) → Gametes → 4 types (RY, Ry, rY, ry) → F1 Generation

• Phenotypic Ratio: 9:3:3:1
• Genotypic Ratio: 1:2:2:4:1:2:1:2:1

Deviations from Mendelism

• Incomplete Dominance: Heterozygote shows intermediate phenotype. Example: Snapdragon Flower (Red × White → Pink)
• Codominance: Both alleles express. Example: AB Blood Group (IAIB)
• Multiple Alleles: More than 2 alleles per gene. Example: ABO system (IA, IB, i)
• Pleiotropy: One gene affects multiple traits. Example: Phenylketonuria → Mental retardation + skin issues
• Polygenic Inheritance: Many genes control one trait → continuous variation. Example: Skin color, Height

ABO Blood Group System

Genotype	Blood Group
IAIA / IAi	A
IBIB / IBi	B
IAIB	AB
ii	O

Note: IA & IB → codominant, i → recessive

Sex Determination & Sex-linked Traits

• Humans → XX/XY
• Birds → ZZ/ZW
• Honey Bee → Haplodiploidy (Male = haploid, Female = diploid)
• X-linked Traits: Mostly in males (XY). Examples: Haemophilia, Colour blindness

Genetic Disorders

• Mendelian Disorders: Thalassemia → Autosomal Recessive
• Chromosomal Disorders:

  Disorder	Cause	Key Feature
  Down Syndrome	Trisomy 21	Mental retardation, short stature
  Turner Syndrome	XO	Female, sterile, short stature
  Klinefelter Syndrome	XXY	Male, tall, sterile

2. Molecular Basis of Inheritance

Discovery of DNA as Genetic Material

• Griffith (1928): Transformation experiment
• Avery, MacLeod & McCarty: DNA responsible for transformation
• Hershey-Chase (1952): DNA enters bacteriophage, protein does not

DNA Structure (Watson & Crick)

• Double helix, antiparallel strands
• Base pairing: A=T, G≡C
• DNA Packaging: DNA + Histones → Nucleosome → Chromatin → Chromosome

DNA Replication (Semi-Conservative)

• Steps:
  1. Origin of Replication (Ori) → replication bubble forms
  2. Helicase unwinds DNA, SSB stabilizes strands
  3. Primase synthesizes RNA primers
  4. DNA Pol III adds nucleotides (Leading continuous, Lagging → Okazaki fragments)
  5. DNA Pol I replaces RNA primers with DNA
  6. DNA ligase joins fragments
  7. Replication terminates

Transcription (DNA → RNA)

• Initiation: RNA polymerase binds promoter, unwinds DNA
• Elongation: RNA synthesized 5’→3’, base pairing: A→U, T→A, G→C, C→G
• Termination: RNA transcript released
• Post-transcriptional modifications (eukaryotes): 5’ cap, 3’ poly-A tail, splicing

Translation (mRNA → Protein)

• Initiation: Small ribosomal subunit + mRNA + tRNA(Met) → Initiation complex
• Elongation: Ribosome moves codon by codon, tRNA brings amino acids, peptide bonds formed
• Termination: Stop codon reached → Release factor → Polypeptide released
• Post-translational modification: Folding, addition of groups, cleavage if necessary

Gene Regulation – Lac Operon

• Lactose Absent → Repressor binds → Gene OFF
• Lactose Present → Repressor removed → Gene ON

DNA Fingerprinting

DNA Sample → Restriction Enzyme → Gel Electrophoresis → Band Pattern → Identification

Applications: Forensics, Paternity Testing

Human Genome Project

DNA Sequencing → Mapping Genes → Genome Database → Applications

3. Evolution

Origin of Life

• Primordial Soup Theory (Oparin)
• Chemical evolution → First prokaryotes

Evidences of Evolution

• Fossils → Geological record
• Comparative Anatomy → Homologous/Analogous structures
• Embryology → Similar embryonic stages
• Molecular Biology → DNA & Protein sequence similarity

Darwinian Natural Selection

Variation → Struggle for Existence → Survival of the Fittest → Evolution

Modern Synthetic Theory: Combines Darwin + Mendelian Genetics

Mechanism of Evolution

• Sources of Variation: Mutation, Recombination
• Types of Natural Selection:
  • Stabilizing → favors mean
  • Directional → favors one extreme
  • Disruptive → favors both extremes
• Other Factors: Gene Flow, Genetic Drift → Population Evolution → Speciation

Adaptive Radiation & Human Evolution

Common Ancestor → Adaptive Radiation → Multiple Species

Human Evolution: Australopithecus → Homo habilis → Homo erectus → Homo sapiens

Hardy-Weinberg Principle

Allele Frequencies: p + q = 1

Genotype Frequencies: p² + 2pq + q² = 1

Conditions: No mutation, No migration, Large population, Random mating, No selection

Conclusion

These comprehensive notes cover all key concepts of Genetics and Evolution for NEET 2026, including Mendelian inheritance, molecular basis of inheritance, gene regulation, DNA fingerprinting, and evolutionary mechanisms. The stepwise flow of replication, transcription, and translation ensures easy understanding and quick revision. Students can use this as a last-minute revision guide to strengthen conceptual clarity and enhance problem-solving skills for NEET exams.

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