Principles of Inheritance and Variation Class 12 Biology | Chapter 4 One Shot NCERT

Aap apne bhai-behen jaise dikhte ho, par photocopy kyun nahi? 😄 Iska jawab hai Genetics! Is video mein poora chapter "Principles of Inheritance and Variation" (Class 12 Biology, NCERT Chapter 4) ek hi video mein: Mendel ke laws, monohybrid & dihybrid cross (Punnett square step-by-step), test cross, incomplete dominance, co-dominance & ABO, chromosomal theory, linkage, sex determination, mutation, pedigree analysis, Mendelian aur chromosomal disorders, rapid revision aur 18 board-style questions. Short notes neeche hain, full PDF notes ka link bhi 👇 CHAPTERS 0:00 Intro: family jaise kyun dikhte hain? 1:35 Genetics, inheritance & variation, Mendel 3:45 True-breeding lines & 7 contrasting traits 5:20 Monohybrid cross: tall × dwarf 8:05 Punnett square: 3:1 & 1:2:1 10:37 Law of Dominance, Law of Segregation, test cross 15:09 Incomplete dominance, co-dominance, ABO blood groups 19:30 Dihybrid cross: 9:3:3:1, independent assortment 23:09 Mendel ka kaam 1900 tak ignore kyun hua? 23:54 Chromosomal theory, linkage & recombination 27:20 Polygenic inheritance & pleiotropy 29:23 Sex determination: XO, XY, ZW, honey bee 33:22 Mutation 34:24 Pedigree analysis & Mendelian disorders 39:38 Chromosomal disorders: Down's, Klinefelter's, Turner's 41:32 Rapid revision 43:15 Quiz: 18 questions 49:56 Outro KEY NOTES • Inheritance = process by which characters are passed on from parent to progeny (basis of heredity); Variation = degree by which progeny differ from their parents • Mendel: hybridisation experiments on garden pea for seven years (1856–1863); first use of statistical analysis and mathematical logic in biology; 14 true-breeding varieties; 7 pairs of contrasting traits • Monohybrid cross (TT × tt): F1 all tall (Tt); F2 phenotypic ratio 3:1, genotypic ratio 1 TT : 2 Tt : 1 tt • Law of Dominance: characters are controlled by discrete units called factors; factors occur in pairs; in a dissimilar pair one member dominates (dominant) the other (recessive) • Law of Segregation: alleles do not blend; during gamete formation the alleles of a pair segregate, so each gamete receives only one of the two • Test cross: organism showing dominant phenotype × recessive parent; 1:1 progeny ratio means the test plant is heterozygous (Tt) • Incomplete dominance: snapdragon (dog flower) RR (red) × rr (white) → F1 Rr pink; F2 1 red : 2 pink : 1 white • Co-dominance: ABO blood groups, gene I with three alleles IA, IB, i (multiple alleles); IA and IB are co-dominant, both completely dominant over i; 6 genotypes, 4 phenotypes (A, B, AB, O) • Dihybrid cross (RRYY × rryy): F2 phenotypic ratio 9:3:3:1 = (3:1) × (3:1) • Law of Independent Assortment: when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair • Mendel's work was published in 1865 and rediscovered in 1900 by de Vries, Correns and von Tschermak • Chromosomal theory of inheritance: Sutton and Boveri (chromosomes and genes behave in parallel); experimental verification by T.H. Morgan on Drosophila melanogaster • Linkage = physical association of genes on a chromosome; recombination = generation of non-parental gene combinations. Morgan: yellow–white 1.3% recombination, white–miniature wing 37.2%. Sturtevant mapped genes using recombination frequency • Polygenic inheritance: traits controlled by three or more genes + environment, e.g. human skin colour. Pleiotropy: one gene, multiple phenotypic effects, e.g. phenylketonuria • Sex determination: XO type (many insects), XY type (humans, Drosophila) = male heterogamety; ZW type (birds) = female heterogamety. Honey bee: haplodiploid, female 32 chromosomes, male (drone) 16 • Humans: 22 pairs of autosomes + XX (female) / XY (male); the sperm decides the sex of the child; 50 per cent probability of a male or female child in each pregnancy • Mutation: alteration of DNA sequences, changing genotype and phenotype; point mutation (sickle-cell anaemia), frame-shift mutation; mutagens such as UV radiations • Pedigree analysis: square = male, circle = female, shaded = affected • Mendelian disorders: haemophilia and colour blindness (sex-linked recessive); sickle-cell anaemia, phenylketonuria, thalassemia (autosomal recessive); myotonic dystrophy (autosomal dominant) • Colour blindness: about 8 per cent of males and 0.4 per cent of females. Sickle-cell: Glu → Val at the 6th position of the β-globin chain (GAG → GUG) • Chromosomal disorders: Down's syndrome (trisomy of 21), Klinefelter's syndrome (47, XXY), Turner's syndrome (45 with X0) 📄 Full PDF notes: [https://drive.google.com/file/d/15z04...] #Class12Biology #InheritanceAndVariation #NCERTBiology #Genetics #PunnettSquare #MendelsLaws #NEET #CBSE #BoardExam #OneShot #SimpleLearningHub