Introduction
Genetics is one of the most important and scoring units of Class 12 Biology, but at the same time, it can feel difficult because of terms, laws, crosses, and numerical problems. That is why most students search for Class 12 Genetics Short Notes PDF before exams.
Short notes help you revise faster, understand concepts clearly, and focus only on exam-relevant points. In this article, you will get complete Genetics short notes, written in a simple language, covering all topics line by line, along with important exam points useful for CBSE / State Boards / NEET foundation.
Class 12 Genetics Short Notes PDF Download | Important Questions 2026
Why Class 12 Genetics Short Notes Are Important?
- Genetics carries high weightage in board exams
- Many direct theory + numericals are asked
- Short notes save time during revision
- Helpful for last-minute preparation
- Easy to remember definitions, laws, and diagrams
Chapters Covered in Class 12 Genetics
Class 12 Genetics includes the following chapters from Biology:
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
All topics below are covered line by line.
Chapter 1: Principles of Inheritance and Variation – Short Notes
1. Genetics
Genetics is the branch of biology that deals with the study of heredity and variation.
- Heredity: Transmission of characters from parents to offspring
- Variation: Differences among individuals of the same species
2. Mendel and His Experiments
Gregor Johann Mendel is known as the Father of Genetics.
- He performed experiments on pea plants (Pisum sativum)
- Chose pea plants because of:
- Short life cycle
- Clear contrasting traits
- Easy cross-pollination
3. Important Genetic Terms
- Gene: Unit of inheritance
- Allele: Alternative form of a gene
- Homozygous: Same alleles (TT or tt)
- Heterozygous: Different alleles (Tt)
- Genotype: Genetic makeup
- Phenotype: Physical appearance
4. Monohybrid Cross
A cross involving one pair of contrasting characters.
- Phenotypic ratio (F₂): 3 : 1
- Genotypic ratio (F₂): 1 : 2 : 1
5. Law of Dominance
- One allele masks the effect of another
- Dominant allele expresses itself in heterozygous condition
6. Law of Segregation
- Alleles separate during gamete formation
- Each gamete carries only one allele
7. Dihybrid Cross
A cross involving two pairs of contrasting characters.
- Phenotypic ratio: 9 : 3 : 3 : 1
- Based on Law of Independent Assortment
8. Law of Independent Assortment
- Genes for different traits assort independently during gamete formation
- Applies only when genes are located on different chromosomes
9. Incomplete Dominance
- Neither allele is completely dominant
- Example: Flower color in snapdragon
- Phenotypic ratio: 1 : 2 : 1
10. Codominance
- Both alleles express equally
- Example: AB blood group
11. Multiple Alleles
- More than two alleles exist for a gene
- Example: ABO blood group system
12. Blood Group Inheritance
- Controlled by three alleles (IA, IB, i)
- IA and IB are codominant
- i is recessive
13. Sex Determination
- Humans follow XX–XY mechanism
- Male determines the sex of the child
14. Genetic Disorders
Mendelian Disorders:
- Haemophilia
- Colour blindness
- Sickle cell anaemia
Chromosomal Disorders:
- Down syndrome (Trisomy 21)
- Turner syndrome (XO)
- Klinefelter syndrome (XXY)
Chapter 2: Molecular Basis of Inheritance – Short Notes
1. DNA as Genetic Material
DNA stores and transmits genetic information.
- Located in nucleus
- Double-stranded helix structure
2. Structure of DNA (Watson and Crick Model)
- Double helix
- Sugar-phosphate backbone
- Complementary base pairing:
- A = T
- G ≡ C
3. RNA as Genetic Material
- Found in some viruses
- Single-stranded
- Less stable than DNA
4. Types of RNA
- mRNA: Carries genetic message
- tRNA: Transfers amino acids
- rRNA: Structural component of ribosomes
5. DNA Replication
- Semi-conservative process
- Occurs during S-phase
- Enzyme: DNA polymerase
6. Transcription
- Formation of RNA from DNA
- Occurs in nucleus (eukaryotes)
7. Genetic Code
- Triplet code
- Universal and degenerate
- Start codon: AUG
- Stop codons: UAA, UAG, UGA
8. Translation
- Protein synthesis from mRNA
- Occurs on ribosomes
9. Gene Regulation (Lac Operon)
- Found in E. coli
- Consists of:
- Promoter
- Operator
- Structural genes
10. Human Genome Project
- Started in 1990
- Completed in 2003
- Mapped entire human DNA
Important Exam Tips for Genetics
- Practice numericals from Mendel crosses
- Learn ratios and laws by heart
- Draw neat diagrams
- Focus on definitions and examples
- Revise short notes daily before exams
Who Should Use These Genetics Short Notes?
- Class 12 Board students
- Last-minute revision students
- NEET foundation aspirants
- Biology weak students
Conclusion
If you are preparing for board exams, Class 12 Genetics Short Notes PDF is the best resource to revise quickly and score high marks. Genetics becomes easy when concepts are short, clear, and exam-focused. Go through these notes regularly, practice questions, and you will feel confident in the exam.
Class 12 Genetics Short Notes PDF Download | Important Questions 2026
1. Who is known as the Father of Genetics?
A. Darwin
B. Watson
C. Mendel
D. Lamarck
✅ Answer: C. Mendel
2. Genetics is the study of:
A. Evolution
B. Environment
C. Heredity and variation
D. Ecology
✅ Answer: C. Heredity and variation
3. The experimental plant used by Mendel was:
A. Wheat
B. Pea plant
C. Maize
D. Rice
✅ Answer: B. Pea plant
4. The phenotypic ratio in a monohybrid cross is:
A. 1 : 1
B. 9 : 3 : 3 : 1
C. 3 : 1
D. 1 : 2 : 1
✅ Answer: C. 3 : 1
5. The genotypic ratio of monohybrid cross is:
A. 3 : 1
B. 1 : 1
C. 9 : 3 : 3 : 1
D. 1 : 2 : 1
✅ Answer: D. 1 : 2 : 1
6. Law of segregation is also known as:
A. Law of purity of gametes
B. Law of dominance
C. Law of inheritance
D. Law of variation
✅ Answer: A. Law of purity of gametes
7. Which cross involves two pairs of contrasting characters?
A. Test cross
B. Back cross
C. Monohybrid cross
D. Dihybrid cross
✅ Answer: D. Dihybrid cross
8. The phenotypic ratio in dihybrid cross is:
A. 3 : 1
B. 1 : 2 : 1
C. 9 : 3 : 3 : 1
D. 1 : 1 : 1 : 1
✅ Answer: C. 9 : 3 : 3 : 1
9. In incomplete dominance, the phenotypic ratio is:
A. 3 : 1
B. 1 : 1
C. 9 : 3 : 3 : 1
D. 1 : 2 : 1
✅ Answer: D. 1 : 2 : 1
10. Example of codominance is:
A. Sickle cell anaemia
B. Snap dragon flower color
C. ABO blood group
D. Pea seed shape
✅ Answer: C. ABO blood group
11. Which blood group is known as universal donor?
A. A
B. B
C. AB
D. O
✅ Answer: D. O
12. Haemophilia is a:
A. Autosomal disorder
B. X-linked recessive disorder
C. Y-linked disorder
D. Chromosomal disorder
✅ Answer: B. X-linked recessive disorder
13. Colour blindness is inherited as:
A. Autosomal dominant
B. Autosomal recessive
C. X-linked recessive
D. Y-linked
✅ Answer: C. X-linked recessive
14. Down syndrome is caused due to:
A. Trisomy 18
B. Trisomy 21
C. Monosomy X
D. XXY condition
✅ Answer: B. Trisomy 21
15. The genetic material in most organisms is:
A. RNA
B. Protein
C. Lipid
D. DNA
✅ Answer: D. DNA
16. Who proposed the double helix model of DNA?
A. Mendel and Morgan
B. Watson and Crick
C. Franklin and Wilkins
D. Darwin and Wallace
✅ Answer: B. Watson and Crick
17. Complementary base pairing in DNA is:
A. A–G and C–T
B. A–U and G–C
C. A–T and G–C
D. A–C and G–T
✅ Answer: C. A–T and G–C
18. The process of copying DNA is called:
A. Translation
B. Transcription
C. Replication
D. Mutation
✅ Answer: C. Replication
19. The start codon in genetic code is:
A. UAA
B. UGA
C. UAG
D. AUG
✅ Answer: D. AUG
20. The stop codon is:
A. AUG
B. GUG
C. UAA
D. CUG
✅ Answer: C. UAA
21. tRNA is also known as:
A. Messenger RNA
B. Ribosomal RNA
C. Adapter molecule
D. Structural RNA
✅ Answer: C. Adapter molecule
22. Lac operon is found in:
A. Humans
B. Virus
C. E. coli
D. Plants
✅ Answer: C. E. coli
23. The Human Genome Project was completed in:
A. 1990
B. 1995
C. 2000
D. 2003
✅ Answer: D. 2003
24. Translation takes place on:
A. Nucleus
B. Mitochondria
C. Ribosomes
D. Golgi body
✅ Answer: C. Ribosomes
25. Which nitrogenous base is not present in DNA?
A. Adenine
B. Guanine
C. Cytosine
D. Uracil
✅ Answer: D. Uracil