Heredity and Variation (वंशागती एवं विविधता) | Class 12 RBSE Biology Chapter 4

This video provides complete coverage of Heredity and Variation (वंशानुगति तथा विविधता) Chapter 4 from Class 12 RBSE Biology. This is a comprehensive study material designed specifically for RPSC competitive exam aspirants and board exam students.
🎯 EXAM IMPORTANCE:
✅ Board Exams: 8-10 marks
✅ RPSC School Lecturer: 10-15 questions
✅ RPSC 1st Grade Teacher: 8-12 questions
✅ RPSC 2nd Grade Teacher: 6-10 questions
✅ REET Level 1 and Level 2: 5-8 questions
📖 COMPLETE TOPICS COVERED:
1. GREGOR MENDEL - FATHER OF GENETICS
Birth and death dates (July 20, 1822 - January 6, 1884)
Experiments on Pisum sativum (Pea plant)
7 contrasting characters selected
Why Mendel chose pea plant
Work published in 1866
Rediscovery in 1900
2. MENDEL'S THREE LAWS OF INHERITANCE
Law of Dominance with examples
Law of Segregation (Purity of Gametes)
Law of Independent Assortment
Monohybrid cross: P, F1, F2 generations
F2 Phenotypic ratio: 3:1
F2 Genotypic ratio: 1:2:1
Dihybrid cross complete explanation
F2 ratio: 9:3:3:1
Punnett square method
3. INCOMPLETE DOMINANCE
Definition and concept
Example: Mirabilis jalapa (Four O'Clock plant)
Cross between Red and White flowers
F1: All Pink (intermediate)
F2 ratio: 1:2:1 (Red:Pink:White)
4. CO-DOMINANCE
Definition with examples
ABO blood group system
Three alleles: IA, IB, i
4 blood groups: A, B, AB, O
6 possible genotypes
Universal donor: O group
Universal recipient: AB group
Rh factor (Rh+ and Rh-)
5. CHROMOSOMAL THEORY OF INHERITANCE
Proposed by Walter Sutton and Theodor Boveri (1902)
Genes located on chromosomes
Supporting evidence
6. SEX DETERMINATION
Human chromosome number: 46 (23 pairs)
Autosomes: 44 (22 pairs)
Sex chromosomes: XX (female), XY (male)
XY system in humans
ZW system in birds
XO system in grasshoppers
Father determines child's sex
Sex ratio: 1:1
7. LINKAGE AND CROSSING OVER
Discovered by Thomas Hunt Morgan (1910)
Complete and incomplete linkage
Crossing over process
Occurs in Pachytene stage
Recombination frequency
Map units and centimorgan
8. MUTATION
Definition by Hugo de Vries (1901)
Somatic vs Germinal mutation
Gene mutation vs Chromosomal mutation
Beneficial, harmful, and neutral mutations
Mutagens: Physical, Chemical, Biological
9. GENETIC DISORDERS
Mendelian Disorders:
Sickle Cell Anemia (Autosomal recessive, Chromosome 11)
Thalassemia (Autosomal recessive)
Hemophilia (X-linked recessive, Factor VIII and IX deficiency)
Color Blindness (X-linked recessive, affects 8% males)
Phenylketonuria/PKU (Autosomal recessive, Chromosome 12)
Chromosomal Disorders:
Down Syndrome (Trisomy 21, Karyotype: 47, +21)
Klinefelter Syndrome (47, XXY in males)
Turner Syndrome (45, XO in females)
Edward Syndrome (Trisomy 18)
Patau Syndrome (Trisomy 13)
10. PEDIGREE ANALYSIS
Symbols and their meanings
Autosomal dominant and recessive patterns
X-linked inheritance patterns
Uses in genetic counseling
11. IMPORTANT SCIENTISTS AND CONTRIBUTIONS
Gregor Mendel (1866) - Laws of Inheritance
Hugo de Vries (1900) - Rediscovered Mendel's work, Mutation
Walter Sutton & Theodor Boveri (1902) - Chromosomal theory
Thomas Hunt Morgan (1910) - Linkage and crossing over
Karl Landsteiner (1900) - ABO blood groups
F.A. Janssens (1909) - Crossing over
12. EXAM-IMPORTANT FACTS AND FORMULAE
Mendel's experimental duration: 7 years (1856-1863)
Number of pea plants used: 28,000
Test cross ratio: 1:1
Back cross definition
Number of phenotypes formula: 2^n
Number of genotypes formula: 3^n
Number of gametes formula: 2^n
Recombination frequency calculation
Barr body discovered by Murray Barr (1949)

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