Principles of Inheritance and Variation – Class 12 Biology Notes | CBSE NCERT Based

 📚 Chapter: Principles of Inheritance and Variation – Class 12 Biology Notes



---


🔸 1. Introduction


Genetics is the branch of biology that deals with heredity and variation.


Heredity: Transmission of characters from parents to offspring


Variation: Differences among individuals




---


🔹 2. Mendel and His Experiments


Gregor Mendel is known as Father of Genetics


He worked on garden pea (Pisum sativum)


He selected 7 contrasting traits like tall/dwarf, round/wrinkled etc.




---


🔹 3. Mendel’s Laws of Inheritance


a) Law of Dominance


Dominant allele expresses itself in F₁ generation



b) Law of Segregation


Alleles separate during gamete formation



c) Law of Independent Assortment


Genes for different traits assort independently




---


🔹 4. Monohybrid Cross


One trait considered


Genotypic ratio: 1:2:1


Phenotypic ratio: 3:1




---


🔹 5. Dihybrid Cross


Two traits considered


Phenotypic ratio: 9:3:3:1




---


🔹 6. Incomplete Dominance


F₁ is intermediate


Example: Red × White flower = Pink (in Snapdragon)




---


🔹 7. Codominance


Both alleles express together


Example: AB blood group (IA + IB = AB)




---


🔹 8. Multiple Allelism


More than 2 alleles control a trait


Example: Blood group – IA, IB, i




---


🔹 9. Sex Determination


XX-XY system in humans


XX = Female, XY = Male


Male determines the sex of baby




---


🔹 10. Genetic Disorders


a) Mendelian Disorders


Haemophilia


Sickle Cell Anaemia


Colour blindness



b) Chromosomal Disorders


Down’s syndrome (Trisomy 21)


Turner’s syndrome (XO)


Klinefelter’s syndrome (XXY)




---


📌 Conclusion:


Genetics helps us understa

nd how traits pass from parents to offspring and why differences occur. Mendel’s work laid the foundation for modern biology and medicine.


📊 Important Diagrams – Principles of Inheritance and Variation


1. ✅ Monohybrid Cross (Mendel's pea plant – single trait cross with 3:1 ratio)



2. ✅ Dihybrid Cross (Two trait cross showing 9:3:3:1 ratio)



3. ✅ Punnett Square (Used to predict genotype/phenotype ratio)



4. ✅ Law of Independent Assortment Diagram

(Visual of how different traits assort independently)



5. ✅ Incomplete Dominance Cross

(Red × White = Pink – Snapdragon example)



6. ✅ Codominance Example

(Blood group inheritance – AB from IA and IB)



7. ✅ Multiple Alleles Diagram

(Blood group chart – IA, IB, i combinations)



8. ✅ Sex Determination in Humans

(XX–XY system via Punnett square)



9. ✅ Pedigree Analysis Chart

(Symbols showing inheritance in family tree)



10. ✅ Chromosomal Disorders Karyotypes




Down's syndrome (47, +21)


Turner’s sy

ndrome (XO)


Klinefelter’s syndrome (XXY)


✍️ Written by: Shahid – Study with Shahid

🔗 Visit: https://shahidnotes12.blogspot.co

m

Comments

Post a Comment

Popular posts from this blog

Sexual Reproduction in Flowering Plants – Class 12 Biology Notes

 🌸 Chapter 2: Sexual Reproduction in Flowering Plants – Class 12 Biology Notes Label: Biology, Class 12, Reproduction --- 🔹 Introduction Reproduction in angiosperms (flowering plants) occurs through sexual reproduction involving flowers, gametes, and fertilization. --- 🌼 Parts of a Typical Flower Part Description Sepals (Calyx) Protects flower in bud stage Petals (Corolla) Bright coloured, attract pollinators Stamens (Androecium) Male reproductive part (Anther + Filament) Carpels (Gynoecium) Female reproductive part (Ovary + Style + Stigma) --- 🧬 Pre-fertilization Events 1. Development of Male Gametophyte Microsporogenesis: Formation of microspores (pollen grains) in anther by meiosis Microspore → Pollen mother cell → Pollen grains Mature pollen: 2 cells – Generative cell & Vegetative cell 2. Development of Female Gametophyte Ovule develops inside ovary Megaspore mother cell → Meiosis → 4 megaspores (1 functional) Embryo sac (female gametophyte): 7 cells, 8 nuclei 1 Egg cel...
Read more

Class 12 Chemistry Chapter 9 – Coordination Compounds Notes (With Important Diagrams)

🧪 Chapter 9: Coordination Compounds – Class 12 Chemistry Notes --- 🔍 Introduction Coordination compounds are chemical compounds composed of a central metal atom/ion bonded to surrounding ligands through coordinate bonds. These compounds play a crucial role in biological systems, industrial catalysis, and analytical chemistry. --- 📌 Important Terms and Definitions Coordination Entity: Central metal atom/ion bonded to a fixed number of ligands. Ligands: Ions or molecules that donate a pair of electrons to the metal. Monodentate: Donates one pair (e.g., Cl⁻, NH₃). Bidentate: Donates two pairs (e.g., ethylenediamine). Polydentate: Donates more than two pairs (e.g., EDTA⁴⁻). Coordination Number: Number of ligand donor atoms attached to central metal. Chelate Complex: Complex formed by polydentate ligands. Coordination Sphere: Part of complex enclosed in square brackets. --- 🧲 Types of Ligands Type Examples Monodentate Cl⁻, CN⁻, NH₃ Bidentate C₂O₄²⁻ (oxalate), en Polydentate EDTA⁴⁻ --- ...
Read more

The d- and f-Block Elements – Class 12 Chemistry Notes | Transition & Inner Transition Elements

 🧪 Chapter 8: The d- and f-Block Elements --- 🔹 Introduction d-block → Groups 3–12 f-block → Lanthanides and actinides Known as transition and inner transition elements --- 🔹 Electronic Configuration General: d-block: (n-1)d¹–¹⁰ ns¹–² f-block: (n-2)f¹–¹⁴ (n-1)d⁰–¹ ns² --- 🔹 Properties of d-block Elements Variable oxidation states Formation of colored compounds Catalytic properties Paramagnetic behavior Complex formation 📌 Diagram: Table of transition elements and their oxidation states --- 🔹 Important Series First transition series: Sc to Zn Second series: Y to Cd Third series: La to Hg (excluding lanthanides) --- 🔹 Lanthanides (4f series) Elements: Ce (58) to Lu (71) Properties: +3 oxidation state common Lanthanide contraction Poor shielding by 4f electrons 📌 Diagram: Lanthanide contraction chart --- 🔹 Actinides (5f series) Elements: Th (90) to Lr (103) Properties: Radioactive +3 to +6 oxidation states Poor shielding, large atomic size 📌 Diagram: f-block placement in per...
Read more