Complete Summary and Solutions for Genetic Disorder – NCERT Class XI Biotechnology, Chapter 8 – Chromosomal Abnormalities, Syndromes, Monogenic and Polygenic Diseases, Pedigree Analysis, Exercises

Comprehensive summary and explanation of Chapter 8 'Genetic Disorder' from the NCERT Class XI Biotechnology textbook, detailing chromosomal abnormalities, famous syndromes (Down, Klinefelter, Turner), monogenic disorders (sickle cell anemia, cystic fibrosis, haemophilia), polygenic disorders (diabetes, hypertension, CHD), mitochondrial inheritance, pedigree analysis, and answers to all textbook exercises and questions.

Updated: 1 week ago

Categories: NCERT, Class XI, Biotechnology, Chapter 8, Genetics, Genetic Disorders, Chromosome Abnormalities, Syndromes, Inheritance, Summary, Questions, Answers
Tags: Genetic Disorder, NCERT, Class 11, Biotechnology, Chromosomal Abnormalities, Syndromes, Monogenic Disorder, Polygenic Disorder, Pedigree Mapping, Mitochondrial Inheritance, Down Syndrome, Klinefelter, Turner, Cystic Fibrosis, Diabetes, Haemophilia, Summary, Chapter 8, Answers, Extra Questions
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Genetic Disorder: Class 11 NCERT Chapter 8 - Ultimate Study Guide, Notes, Questions, Quiz 2025

Genetic Disorder

Chapter 8: Biotechnology - Ultimate Study Guide | NCERT Class 11 Notes, Questions, Examples & Quiz 2025

Full Chapter Summary & Detailed Notes - Genetic Disorder Class 11 NCERT

Overview & Key Concepts

  • Chapter Goal: Explore genetic disorders caused by chromosomal abnormalities, single-gene mutations, and multiple genes; understand syndromes, pedigree analysis, and inheritance patterns. Exam Focus: Structural/numerical abnormalities, monogenic types (autosomal/X-linked), polygenic examples, diagrams like karyograms (Fig 8.2), pedigrees (Fig 8.7-8.10). 2025 Updates: Emphasis on diagnostic tools (amniocentesis, Barr body), mitochondrial inheritance (Box 2), real-world famous cases (Box 1). Fun Fact: Down syndrome life expectancy rose from 9 to 60 years due to biotech advances. Core Idea: Disorders arise from gene/chromosome errors; pedigree maps inheritance. Real-World: Genetic counseling prevents transmission; CRISPR targets monogenic fixes. Ties: Links to cell division (Ch2), biomolecules (Ch3), inheritance principles (Ch6). Expanded: All subtopics (8.1-8.3) covered point-wise with diagram descriptions, examples, and clinical insights for visual/holistic learning.
  • Wider Scope: From chromosomal (aneuploidy/polyploidy) to monogenic (Mendelian patterns) and polygenic (multifactorial); includes diagnosis/treatment, boxes on celebs/mitochondria.
  • Expanded Content: Detailed on causes (radiation/mutation), symptoms, karyotypes, inheritance diagrams, polyploid plants in food, mitochondrial maternal transmission.
Fig. 8.1: Structural chromosomal abnormalities (Description)

(a) Deletion: Shortened chromosome (A-B-C-D-E-F → A-C-D-E-F). (b) Duplication: Repeated segment (A-B-C-D-E-F → A-B-C-B-C-D-E-F). (c) Inversion: Reversed orientation (A-B-C-D-E-F → A-F-E-D-C-B). (d) Translocation: Segment swap (Chrom1 A-B to Chrom2 L-P → A-B-L-M-N-O-P; reciprocal exchange). Visual: Labeled chromosome arms with breaks/arrows.

8.1 Chromosomal Abnormalities and Syndromes

  • Causes: Environmental (radiation/food) or internal; lead to structural (aberrations) or numerical changes; result in phenotypic diseases/syndromes (group of symptoms vs. disease as physiological response).
  • Numerical Abnormalities: Aneuploidy (monosomy 2n-1, trisomy 2n+1, e.g., trisomy X); polyploidy (full sets multiplied, e.g., 3n=69 triploid banana, 6n=42 hexaploid wheat, 8n=56 octoploid strawberry/sugarcane; useful in agriculture for larger yields).
  • Structural Abnormalities: Changes without number alteration; significant phenotypic impact.

8.1.1 Structural Chromosomal Abnormalities

  • Deletion: Segment breaks off, shortens chromosome; e.g., retinoblastoma (del in chr13); ring chromosome if ends reattach.
  • Duplication: Segment repeats, lengthens chromosome; e.g., Charcot-Marie-Tooth (dup on chr17).
  • Inversion: Segment breaks, reverses 180°, reattaches (length same, gene order flipped); e.g., RCAD syndrome (inv on chr17).
  • Translocation: Segment breaks, attaches to another chromosome; reciprocal (mutual swap, e.g., Burkitt’s lymphoma chr8-14); Robertsonian (non-mutual, reduces chr number, Fig 8.1d).
Fig. 8.2: Karyograms (Description)

(a) Down syndrome: 47,XX,+21 (extra chr21, trisomy). (b) Klinefelter: 47,XXY (extra X in male). Visual: Arranged chromosomes with highlighted abnormality.

8.1.2 Numerical Chromosomal Abnormalities (Syndromes)

  • Down's Syndrome (Trisomy 21): Incidence 1/800 births; cause: nondisjunction (chr fail to separate in meiosis); karyotype 47,XX/XY,+21; risk ↑ with maternal age (>35 yrs, 85% cases); symptoms: flat face, slanting eyes, small mouth, protruding tongue, flattened nose, short neck/arms/legs, single palmar crease, low IQ, hypotonia, underdeveloped gonads, heart/breathing/hearing issues; diagnosis: karyotype; treatment: tailored (speech/physio/nutrition); life expectancy: 9 yrs (1900s) to 60+ now.
  • Klinefelter's Syndrome (XXY): Incidence 1/1000 males; cause: nondisjunction in meiosis (XX ovum + Y sperm); karyotype 47,XXY; not inherited from father; symptoms: tall stature, reduced hair, small testes, enlarged breasts, coarse voice, osteoporosis, small penis, feminine abdomen (Fig 8.3); diagnosis: Barr body in buccal smear (1 Barr = extra X); treatment: testosterone for masculinity, counseling for depression/aggression; noticeable at puberty.
  • Turner's Syndrome (Monosomy X): Incidence 1/2500 girls (common in miscarriages); cause: nondisjunction (no-X ovum + X sperm); karyotype 45,X; not inherited; symptoms: short stature, webbed neck, small breasts, low-set ears, swollen hands/feet, underdeveloped ovaries, absent menses (Fig 8.4); diagnosis: prenatal (amniocentesis/chorionic sampling), Barr body absence; treatment: hormone therapy (androgen/estrogen) for growth/ovarian function; no cure.

Box 1: Famous People with Syndromes (Real-World Inspiration)

  • Isabelle Springmühl: Down syndrome fashion designer; overcame rejections, showcased in London/Rome/Mexico.
  • George Washington: Likely Klinefelter (tall, childless, adopted kids).
  • Lauren Foster: XXY Klinefelter model; transitioned female, Vogue feature, Miss SA attempt.
  • Linda Hunt: Turner actress; Oscar winner (1984), 13 awards including Teen Choice 2012.
  • Dr. Catherine Ward Melver: Turner geneticist (4'8"), adopted Turner child Zoe from China.

Tip: Relate to resilience; use for essay motivation.

8.2 Monogenic Disorders and Pedigree Mapping (Cystic Fibrosis, Sickle Cell Anemia, Haemophilia, Color Blindness)

  • Overview: >10,000 monogenic diseases affect millions; caused by single gene error; symptoms depend on gene function; follow Mendel's laws (spontaneous mutations possible); >200 mutations in CFTR gene for cystic fibrosis.
  • Classification: Autosomal recessive/dominant, X-linked recessive/dominant.
  • Pedigree Analysis: Family tree interpretation for inheritance; symbols (Fig 8.5): square (male), circle (female), filled (affected), horizontal (mating), vertical (offspring), Roman (generations), Arabic (order), diamond (unknown), twin symbols.
Fig. 8.5: Pedigree Symbols (Description)

Square: Male; Circle: Female; Filled: Affected; Horizontal line: Mating; Vertical: Offspring; I/II: Generations; 1/2: Order; Identical twins: Joined top; Non-identical: Separate. Visual: Standard icons for quick mapping.

Autosomal Recessive Disorders

  • Concept: Needs 2 defective alleles (homozygous); carriers (heterozygous) unaffected; humans carry ~5+ such genes; e.g., sickle cell anemia (Hb-β gene chr11 mutation → defective Hb clusters post-O2 → sickle RBCs, Fig 8.6; genotype s/s affected, S/s carrier; Fig 8.7 cross: Carriers → 1/4 affected; common in Africa/India Deccan).
  • Other Examples: Cystic fibrosis (thick mucus → lung damage); Tay-Sachs (hexosaminidase A absence → brain fat buildup, fatal childhood, 1/27 Ashkenazi Jews); PKU (phenylalanine hydroxylase mutation → high phenylalanine).
Fig. 8.6: Sickled RBCs (Description)

Peripheral blood smear: Normal round RBCs vs. stiff sickle-shaped under low O2. Visual: Microscope image with rod-like Hb structures.

Fig. 8.7: Sickle Cell Pedigree Cross (Description)

Carrier parents (S/s) → Gametes S/s → Offspring: S/S normal, S/s carrier, s/s affected (1:2:1 genotypic, 3:1 phenotypic). Visual: Punnett square with family tree.

Autosomal Dominant Disorders

  • Concept: One defective allele (heterozygous) causes; normal recessive; e.g., Achondroplasia (dwarfism, Fig 8.8; d/d normal, D/d mild dwarf, D/D lethal; most survivors heterozygous); Huntington's (nervous system degeneration).
Fig. 8.8: Achondroplasia Dwarfism (Description)

Schematic: Short limbs, normal trunk/head; genotype D/d. Courtesy: Shutterstock (dwarfism vector). Visual: Proportion comparison normal vs. dwarf.

X-linked Recessive Disorders

  • Concept: Mother carrier (heterozygous X); males affected (hemizygous XY); no father-son transmission, all daughters carriers (Fig 8.9); e.g., Hemophilia (factor VIII/IX mutation → poor clotting, bleeding); DMD (dystrophin mutation → muscle weakness).
Fig. 8.9: X-linked Recessive Inheritance (Description)

Carrier mother (X^H X^h) x normal father (X^H Y) → 50% sons affected, 50% carrier daughters. Visual: Pedigree with criss-cross pattern.

X-linked Dominant Disorders

  • Concept: Affected father → all daughters affected, no sons; affected mother → 50% sons/daughters (Fig 8.10); e.g., Hypophosphatemia (vitamin D rickets); Alport syndrome (hearing/kidney loss).
Fig. 8.10: X-linked Dominant Inheritance (Description)

(a) Affected father: All daughters affected, sons unaffected. (b) Affected mother: 50% affected sons/daughters. Visual: Pedigrees showing transmission.

Exam Case Studies

Sickle cell: Deccan prevalence, carrier screening; Hemophilia: Royal pedigree analysis.

8.3 Polygenic Disorders (Hypertension, Coronary Heart Disease, Diabetes)

  • Concept: Multiple genes + environment; not Mendelian; e.g., hypertension (high BP risk for heart/stroke/renal; stages: Normal <120/80, Elevated 120-129/<80, Stage1 130-139/80-89, Stage2 ≥140/≥90 mmHg).
  • Coronary Heart Disease (CHD): Atherosclerosis narrows coronary artery → ischemia (O2 lack to heart muscle, Fig 8.11); previously "ischaemic heart disease"; fatty plaque buildup.
  • Diabetes Mellitus: Hyperglycemia; Type1 (10%, beta cell destruction, insulin-dependent); Type2 (90%, impaired secretion/resistance, non-insulin dependent); insulin transports glucose to cells.
Fig. 8.11: CHD Heart/Artery (Description)

(a) Normal: Open coronary, no plaque. (b) Diseased: Narrowed artery with fat plaque, reduced blood flow. Visual: Side-by-side heart diagrams with labels.

Box 2: Mitochondrial Inheritance & Diseases

  • Mitochondria: Energy (ATP) via enzymes coded by mtDNA (circular, maternal inheritance; sperm low mt).
  • Diseases: Severity by normal/abnormal mt ratio; affects high-energy organs (brain/heart); father cannot transmit (Fig 8.12).
Fig. 8.12: Mitochondrial Inheritance (Description)

Grandmother faulty mt → Affected son/daughter; unaffected daughter → All offspring affected (maternal line). Visual: Family tree with mt icons (normal/faulty).

Summary

  • Chromosomal (structural/numerical) → syndromes; monogenic → Mendelian patterns via pedigree; polygenic → multifactorial; mitochondrial maternal. Interlinks: To Ch6 inheritance, Ch9 diagnostics.

Key Themes & Tips

  • Aspects: Aneuploidy vs. polyploidy, recessive carrier risks, polygenic environment role.
  • Tip: Mnemonic for structures (DDIT: Deletion-Duplication-Inversion-Translocation); practice pedigrees for ratios.

Project & Group Ideas

  • Map family pedigree for trait.
  • Debate: Genetic screening ethics.
  • Research: CRISPR for monogenic fixes.