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Samacheer Kalvi 10th Science Chapter 21 Long Answer Questions — Breeding and Biotechnology with Answers

Long answer questions (5 marks) from Samacheer Kalvi Class 10 Science Chapter 21 Breeding and Biotechnology with detailed answers.

Updated 25 May 202618 min read
Question 1: Describe plant and animal breeding methods used for crop and livestock improvement.

Answer:

Breeding is the controlled reproduction of organisms to develop new varieties or strains with desired characteristics. It can be traditional (conventional breeding) or modern (using biotechnology).

Plant Breeding:

Objectives of Plant Breeding:

  • Increase crop yield
  • Improve nutritional quality
  • Develop resistance to pests, diseases, drought, and salinity
  • Earlier maturation (shorter growing season)
  • Improve mechanical harvesting characteristics

Methods of Plant Breeding:

1. Introduction:
Answer
  • Collection of plants or seeds from different parts of the world and growing them in a new location
  • Simplest method; no crossing involved
  • e.g., Introduction of Mexican semi-dwarf wheat varieties (Sonalika, Kalyan Sona) to India during the Green Revolution
2. Selection:
Answer
  • Choosing plants with desirable characteristics from a mixed population
  • Mass selection: Select many plants with the desired trait; collect seeds and grow; repeat for several generations
  • Pure line selection: Select a single self-pollinating plant; all offspring are genetically identical → pure line variety
  • e.g., NP4 wheat variety developed by pure line selection
3. Hybridisation (Crossing):
Answer

1. Select parent plants with complementary desirable traits 2. Emasculation: Remove anthers from the female parent (to prevent self-pollination) 3. Bagging: Cover emasculated flowers to prevent unwanted pollen contamination 4. Cross-pollination: Collect pollen from the male parent and apply to stigma of female parent 5. Select offspring with best combination of traits 6. Further selection and crossing over several generations

  • Cross-pollination of two different varieties/species to combine their desirable traits in the offspring
  • Intraspecific hybridisation: Within the same species (most common)
  • Interspecific hybridisation: Between species of the same genus
  • Intergeneric hybridisation: Between different genera (less common)
  • Process:
  • e.g., Saccharum officinarum (thick stem, high sugar) x Saccharum spontaneum (disease resistant, ratooning) → modern sugarcane varieties
  • e.g., IR-8 rice variety (Green Revolution rice — high-yielding, semi-dwarf)
4. Mutation Breeding:
Answer
  • Induced mutations using mutagens (X-rays, gamma rays, UV radiation, chemical mutagens like colchicine, EMS)
  • Mutations are mostly harmful but rare useful mutations can be selected
  • e.g., Sharbati Sonora wheat (golden colour, better chapati quality) — produced by radiation-induced mutation
  • e.g., Atomita varieties of rice (induced mutation)
5. Polyploidy:
Answer
  • Some plants with extra sets of chromosomes (polyploids) have improved traits
  • Colchicine (inhibits spindle formation) can induce polyploidy
  • e.g., Seedless watermelon (triploid, 3n) produced by crossing tetraploid (4n) x diploid (2n)
  • Natural polyploids: Wheat (hexaploid, 6n)
6. Marker-Assisted Selection:
Answer
  • Use of DNA markers (molecular markers linked to desirable genes) to select plants with desired traits without waiting for the plants to express those traits
  • Faster and more precise than traditional selection

Animal Breeding:

Objectives: Increase milk production, meat yield, egg production; improve disease resistance; faster growth; better fibre quality.

Methods of Animal Breeding:

1. Inbreeding:
Answer
  • Mating between closely related animals within the same breed for 4–6 generations
  • Benefits: Accumulates desirable alleles; establishes true-breeding lines; increases homozygosity
  • Problems: Inbreeding depression — reduced fertility, smaller body size, susceptibility to disease due to accumulation of harmful recessive alleles
2. Outbreeding:
Answer
  • Mating between unrelated animals
  • Outcrossing: Mating of animals of the same breed but with no common ancestors for 4–6 generations; corrects inbreeding depression
  • Crossbreeding: Mating animals of different breeds to combine their best traits
  • e.g., Jersey (high milk fat) x Sahiwal (heat-tolerant) → high-yielding heat-tolerant dairy cattle in India
  • Interspecific hybridisation: Cross between different species
  • e.g., Mule = Male donkey x Female horse (superior draft animal — combines strength and endurance)
  • e.g., Hinny = Male horse x Female donkey
3. Artificial Insemination (AI):
Answer
  • Semen from a superior male is collected, stored (often frozen in liquid nitrogen), and artificially introduced into the female's reproductive tract
  • Allows one superior male to father thousands of offspring per year
  • e.g., A single elite bull's semen can be used to inseminate cows across India simultaneously
  • Important in cattle and poultry breeding
4. Multiple Ovulation Embryo Transfer (MOET):
Answer
  • Superior cows are treated with hormones → produce multiple eggs → artificially inseminated
  • Multiple embryos are flushed from the donor cow → transplanted into surrogate mothers
  • Allows a genetically superior cow to produce more than 40 calves per year
  • Used for rapid multiplication of superior stock
Question 2: Explain the steps of recombinant DNA technology. Describe how human insulin is produced using this technology.

Answer:

Recombinant DNA technology (genetic engineering) is the set of techniques used to isolate, manipulate, combine, and express genes from different organisms. It was developed in the early 1970s (Cohen and Boyer, 1973).

Tools Required in Recombinant DNA Technology:

1. Restriction Enzymes (Molecular Scissors):
Answer
  • Bacterial enzymes that recognise and cut DNA at specific short sequences (recognition sites, usually 4–8 base pairs long)
  • e.g., EcoRI cuts DNA at the sequence 5'–GAATTC–3' between G and A, creating "sticky ends"
  • Over 3,000 restriction enzymes are known
  • Allow precise cutting of DNA at specific locations
2. DNA Ligase (Molecular Glue):
Answer
  • Joins (ligates) DNA fragments together by forming phosphodiester bonds
  • Used to insert the gene of interest into the vector
3. Vectors:
Answer
  • DNA molecules that carry the gene of interest into the host cell
  • Must be able to replicate in the host cell
  • Types of vectors:
  • Plasmids: Small circular DNA molecules in bacteria; most commonly used vector
  • Bacteriophages: Viruses that infect bacteria
  • Cosmids, BACs (Bacterial Artificial Chromosomes): For larger inserts
  • Retroviral vectors: For gene therapy in humans
4. Host Organism:
Answer
  • The organism that takes up the recombinant DNA and expresses it
  • Commonly used: Escherichia coli (bacteria), Saccharomyces cerevisiae (yeast), insect cells, mammalian cells

Steps of Recombinant DNA Technology:

Step 1: Isolation of the Gene of Interest

  • The gene to be cloned is identified and isolated from the donor organism's genome
  • Method A: Cut the donor organism's DNA using restriction enzymes
  • Method B (preferred for eukaryotic genes): Extract mRNA for the protein of interest → synthesise complementary DNA (cDNA) using reverse transcriptase → this avoids introns (non-coding sequences that bacteria cannot process)

Step 2: Preparation of the Vector

  • The vector (usually a plasmid) is cut open with the same restriction enzyme used to cut the gene of interest
  • This creates compatible sticky ends on both the gene and the vector

Step 3: Ligation — Making Recombinant DNA

  • The gene of interest is mixed with the cut vector
  • DNA ligase joins the gene into the vector through the complementary sticky ends
ResultA recombinant DNA (rDNA) molecule containing the gene of interest within the vector

Step 4: Transformation — Introduction into Host Cell

  • The recombinant plasmid is introduced into the host cell (usually E. coli)
  • Methods: Heat shock (briefly heating bacteria in presence of calcium chloride), electroporation (brief electric pulse opens cell membrane pores), microinjection

Step 5: Selection of Transformed Cells

  • Not all host cells take up the recombinant DNA; need to identify which ones did
  • Methods using selectable markers:
  • Antibiotic resistance genes on the plasmid (e.g., ampicillin resistance): transformed cells survive on antibiotic media; untransformed cells die
  • Blue-white screening: The gene is inserted into the lacZ gene of the plasmid; colonies with the gene are white (lacZ disrupted, can't produce blue colour); colonies without the insert are blue

Step 6: Propagation (Cloning)

  • Selected transformed bacteria are grown in large fermenters (bioreactors)
  • As bacteria replicate, they copy the recombinant plasmid → billions of copies of the gene

Step 7: Expression

  • The gene is expressed — bacteria produce the desired protein
  • Conditions are optimised for maximum protein production

Step 8: Extraction and Purification

  • The desired protein is extracted from the bacterial culture
  • Purified using chromatography techniques
  • Quality control testing before use

Production of Human Insulin Using Recombinant DNA Technology:

Before 1982, insulin for diabetes treatment was extracted from the pancreas of pigs and cattle (animal insulin), which caused allergic reactions in some patients and was expensive.

Step 1: Identify the human insulin gene. Human insulin is encoded by a gene on chromosome 11. It codes for preproinsulin, which is processed into two chains: A chain (21 amino acids) and B chain (30 amino acids) connected by C peptide.

Step 2: Synthesise cDNA for each insulin chain (A and B) from the mRNA, using reverse transcriptase.

Step 3: Insert each cDNA into a separate plasmid vector (in the USA, Genentech used E. coli; modern methods also use yeast).

Step 4: Transform E. coli with the recombinant plasmids. The bacteria produce the A and B chain proteins separately as fusion proteins with beta-galactosidase.

Step 5: Extract the fusion proteins, cleave the insulin chains chemically (cyanogen bromide treatment).

Step 6: Mix the A and B chains under conditions that allow the correct disulfide bonds to form between them → active human insulin.

Step 7: Purify and quality-test.

ResultHumulin (recombinant human insulin) — first approved recombinant DNA pharmaceutical (1982, by Eli Lilly). Identical to natural human insulin, no allergic reactions, can be produced in unlimited quantities.
Question 3: Explain the steps of the Polymerase Chain Reaction (PCR) and its applications.

Answer:

PCR (Polymerase Chain Reaction):

Definition: PCR is an in vitro (in a test tube) technique used to amplify (make millions or billions of copies of) a specific target DNA sequence from a small starting sample. It was invented by Kary Mullis in 1983 (Nobel Prize in Chemistry, 1993).

Components Required for PCR:

1. Template DNA: The DNA containing the target sequence to be amplified (even tiny amounts from a single cell are sufficient) 2. Primers: Two short, single-stranded DNA oligonucleotides (typically 15–25 bases long), one complementary to each strand of the template at the boundaries of the target sequence. They define what is amplified. 3. Taq DNA Polymerase: A heat-stable DNA polymerase from the thermophilic bacterium Thermus aquaticus (lives in hot springs). Remains active even at the high temperatures used in PCR. 4. dNTPs (Deoxynucleotide Triphosphates): The building blocks of DNA (dATP, dGTP, dCTP, dTTP) 5. Buffer solution: Optimal ionic conditions for the enzyme 6. MgCl2: Cofactor for Taq polymerase

Steps of PCR (One Cycle = Three Steps):

Step 1: Denaturation (94–96°C, ~30 seconds)

  • The reaction mixture is heated to high temperature (94–96°C)
  • The hydrogen bonds between the two strands of double-stranded template DNA break
  • The DNA strands separate (denature) into two single-stranded templates

Step 2: Annealing (50–65°C, ~30 seconds)

  • The temperature is lowered to allow primers to bind (anneal) to their complementary sequences on the single-stranded template DNA
  • The annealing temperature depends on the primer sequence (usually 5°C below the melting temperature of the primers)
  • The two primers bind to opposite strands, flanking the target sequence
  • This defines the region of DNA to be amplified

Step 3: Extension / Elongation (72°C, ~1 minute per kb)

  • Temperature is raised to 72°C — the optimal temperature for Taq polymerase activity
  • Taq DNA polymerase binds to the primer-template junction and synthesises a new complementary DNA strand
  • It adds dNTPs in the 5' to 3' direction, extending from each primer
  • Each template strand produces a new complementary strand
ResultTwo double-stranded DNA molecules from one → DNA is doubled

PCR Cycles:

  • The cycle (denaturation → annealing → extension) is repeated 25–40 times
  • After each cycle, the number of copies doubles
  • After n cycles: 2n copies are produced
  • After 30 cycles: approximately 1 billion (2^30 = 1.07 × 10^9) copies of the target sequence

PCR Machine:

  • A thermocycler is used — it automatically and precisely controls temperature changes through the programmed cycles

Applications of PCR:

1. Forensic Science (DNA Fingerprinting):
Answer
  • PCR amplifies tiny amounts of DNA from crime scene samples (blood stain, hair, saliva, skin cells)
  • Amplified DNA is then analysed for Short Tandem Repeats (STRs) or other markers
  • Used for identification of criminals, identification of victims, paternity testing
2. Medical Diagnosis:
Answer
  • Detection of viral and bacterial infections directly from patient samples:
  • HIV diagnosis (PCR to detect HIV RNA)
  • COVID-19 diagnosis (RT-PCR to detect SARS-CoV-2 RNA)
  • Tuberculosis, Hepatitis B and C, herpes, chlamydia
  • Detection of genetic mutations (cancer diagnosis, prenatal diagnosis of genetic disorders)
3. Prenatal Genetic Diagnosis:
Answer
  • PCR on a few cells from amniocentesis or chorionic villus sampling can detect genetic disorders (Down syndrome, cystic fibrosis, sickle cell anaemia)
4. Paternity Testing:
Answer
  • Compare specific DNA markers between the child and alleged father
5. Research:
Answer
  • Amplification of genes for cloning, sequencing, mutation analysis
  • Gene expression studies
6. Archaeology and Palaeontology:
Answer
  • Amplification of ancient DNA from fossils, mummies, dried specimens
  • e.g., Analysis of Neanderthal DNA, woolly mammoth DNA
7. Plant and Animal Breeding:
Answer
  • Identification of disease-resistance genes, quality genes for marker-assisted selection
Question 4: Describe the process of cloning animals. Explain with reference to Dolly, the sheep.

Answer:

Animal Cloning:

Definition: Cloning is the production of genetically identical copies of an organism. In animals, it is achieved through Somatic Cell Nuclear Transfer (SCNT) — transferring the nucleus from a somatic (body) cell into an enucleated egg cell.

Types of Animal Cloning:

1. Reproductive Cloning:
Answer
  • Goal: Produce a live animal genetically identical to the donor of the nucleus
  • e.g., Dolly the sheep (first cloned mammal from an adult somatic cell)
2. Therapeutic Cloning:
Answer
  • Goal: Produce embryonic stem cells genetically matched to a patient for medical treatment
  • The embryo is not allowed to develop into a live animal
  • Stem cells from the cloned embryo can differentiate into any cell type for treating diseases
  • No longer the only stem cell approach — induced Pluripotent Stem Cells (iPSCs) are now used instead

Dolly the Sheep — The First Mammal Cloned from an Adult Somatic Cell:

Scientists: Ian Wilmut, Keith Campbell, and colleagues at the Roslin Institute, Edinburgh, Scotland.

Year: Dolly was born on 5 July 1996; the research was published in February 1997. She was named after the country singer Dolly Parton.

Procedure (Somatic Cell Nuclear Transfer — SCNT):

Step 1: Donor Nucleus

  • A somatic (body) cell — specifically a mammary gland cell — was taken from a 6-year-old adult Finn Dorset white sheep (nuclear donor)
  • These cells were cultured in the laboratory and then starved of nutrients (serum-deprived) to arrest cell division in the G0 phase — this synchronises the cell cycle, which is essential for successful nuclear transfer

Step 2: Enucleated Egg Cell

  • An unfertilised egg cell (oocyte) was obtained from a Scottish Blackface sheep (egg donor)
  • The nucleus was removed from the egg cell by micromanipulation (enucleation) — creating an enucleated egg (cytoplast)

Step 3: Cell Fusion / Nuclear Transfer

  • The enucleated mammary gland cell was placed next to the enucleated egg cell
  • They were fused together using an electric pulse (electrofusion) — this both fused the cells and activated the egg to begin development
  • The nucleus of the mammary cell is now inside the egg cytoplasm — a "reconstructed embryo"

Step 4: Activation and Development

  • The reconstructed embryo was stimulated to divide and develop (the egg cytoplasm reprogrammed the somatic cell nucleus back to a totipotent embryonic state)
  • The embryo developed in culture to the blastocyst stage

Step 5: Implantation

  • The blastocyst was implanted into the uterus of a surrogate mother (another Scottish Blackface sheep)
  • The surrogate carried the pregnancy to term
Result
  • Dolly was born with white wool (like the Finn Dorset donor), not black-faced like the surrogate or the egg donor
  • DNA testing confirmed she was genetically identical to the Finn Dorset mammary cell donor
  • Dolly successfully reproduced naturally (had 6 lambs), demonstrating that she was a fully functional animal

Significance of Dolly: 1. First proof that the nucleus from an adult, fully differentiated somatic cell can be reprogrammed to be totipotent (can direct the development of a complete organism) 2. Overturned the previous belief that differentiation was irreversible 3. Opened the field of nuclear reprogramming and led eventually to iPSC technology

Dolly's health: Dolly was euthanised on 14 February 2003 at age 6.5 (Finn Dorset sheep normally live to 11–12 years). She had developed progressive lung disease and arthritis. Some scientists suggested she aged prematurely — the Finn Dorset donor was 6 years old, so her telomeres were already shortened.

Other Cloned Animals:

  • Cattle, pigs, horses, cats, dogs, mice have all been cloned
  • Endangered species cloning attempts: Gaur (cloned 2001, died of infections), Banteng (lived, 2003)
  • No confirmed human cloning (major ethical, legal, and scientific barriers)

Ethical Issues:

  • Reproductive human cloning is banned in virtually all countries
  • Therapeutic cloning raises ethical debates about the status of human embryos
  • Low efficiency of SCNT (Dolly required 277 attempts)
  • Health problems in cloned animals (epigenetic abnormalities)
Question 5: Explain tissue culture in plants and describe the applications of biotechnology in agriculture.

Answer:

Plant Tissue Culture (Micropropagation):

Definition: Plant tissue culture is the technique of growing isolated plant cells, tissues, or organs on an artificial nutrient medium under aseptic (sterile) conditions.

Basis: Plant cells are totipotent — each living cell contains the full genetic information to regenerate a whole plant.

History: F.C. Steward (1950s) grew a complete carrot plant from single root cells — demonstrated totipotency.

Basic Technique of Plant Tissue Culture:

Step 1: Selection of Explant

  • An explant is the plant tissue used to initiate tissue culture
  • Can be any part: leaf, root tip, stem, seed, embryo, pollen grain, bud
  • Younger, rapidly dividing tissues give best results
  • Must be free from disease

Step 2: Surface Sterilisation

  • The explant is surface sterilised to remove all microorganisms
  • Methods: 70% ethanol wash, sodium hypochlorite (bleach) solution, followed by multiple sterile water washes

Step 3: Nutrient Medium

  • Murashige and Skoog (MS) medium — most commonly used
  • Contains: macronutrients (N, P, K, Ca, Mg, S), micronutrients, vitamins, sugar (sucrose — energy source), plant growth regulators (phytohormones)
  • Auxins (e.g., 2,4-D, IAA): Promote root formation and callus formation
  • Cytokinins (e.g., Kinetin, BAP): Promote shoot formation and cell division
  • Ratio of auxin to cytokinin determines the developmental pathway:
  • High auxin:cytokinin → roots
  • Low auxin:cytokinin → shoots
  • Equal → callus

Step 4: Callus Formation

  • The explant placed on nutrient medium with high auxin → dedifferentiates into an undifferentiated mass of cells called a callus
  • Callus cells are actively dividing

Step 5: Organogenesis (Shoot and Root Formation)

  • Callus on medium with high cytokinin → develops shoots (shoot organogenesis)
  • Alternatively, single callus cells can be cultured in liquid medium → embryoids (somatic embryos) → plantlets

Step 6: Acclimatisation

  • Test tube plantlets are gradually transferred from sterile conditions to greenhouse, then to field
  • They need time to adjust from high humidity and artificial light to normal conditions

Applications of Biotechnology in Agriculture:

1. Genetically Modified (GM) Crops / Transgenic Crops:
Answer

A transgenic plant contains a gene (transgene) from another organism, introduced through recombinant DNA technology.

  • Bt Crops (Bacillus thuringiensis crops):
  • The cry gene from Bacillus thuringiensis (a soil bacterium) encodes Bt toxin proteins
  • Bt toxin is lethal to certain insect pests but harmless to humans and non-target organisms
  • Bt Cotton: The cry1Ac gene was inserted → cotton plants produce Bt toxin in leaves and bolls → controls bollworm (Helicoverpa armigera), the most damaging cotton pest → dramatically reduced insecticide use
  • Bt Cotton is widely grown in India (over 90% of Indian cotton area)
  • Bt Brinjal (eggplant): Controls brinjal shoot and fruit borer; approved in Bangladesh
  • Herbicide-Tolerant Crops (e.g., Roundup Ready Soybean):
  • Gene for tolerance to the herbicide glyphosate (Roundup) inserted into soybean
  • Farmers can spray glyphosate to kill weeds without harming the crop
  • Controversial: concerns about herbicide-resistant "superweeds"
  • Virus-Resistant Crops:
  • Coat protein gene of virus inserted into plant → plant produces the protein and becomes resistant to the virus
  • e.g., Virus-resistant papaya (Rainbow papaya) in Hawaii saved the papaya industry from Papaya Ringspot Virus
  • Golden Rice:
  • Rice engineered to produce beta-carotene (precursor of Vitamin A) in the grain
  • Normal rice does not produce beta-carotene in the endosperm
  • Intended to combat Vitamin A deficiency (leading cause of blindness in children in developing countries)
  • Contains the phytoene synthase gene from daffodil and a lycopene beta-cyclase gene
  • Currently under regulatory review
2. Micropropagation for Crop Production:
Answer
  • Rapid production of pathogen-free planting material
  • e.g., Banana, potato, sugarcane, ornamental plants produced in millions via tissue culture
  • Disease-free plants: Meristem culture used to eliminate viruses (viruses don't infect meristematic cells)
3. Biofertilisers:
Answer
  • Nitrogen-fixing bacteria (Rhizobium, Azotobacter) and mycorrhizal fungi applied to soil/seeds
  • Rhizobium introduced into legume root nodules fixes atmospheric nitrogen
  • Reduces chemical fertiliser use
4. Biopesticides:
Answer
  • Bt spray (Bacillus thuringiensis) as a biopesticide alternative to chemical pesticides
  • Safer for the environment and non-target organisms
5. Marker-Assisted Breeding:
Answer
  • Use molecular markers (linked to useful genes) to select crop plants with disease resistance, drought tolerance, or quality traits more efficiently
6. Bioremediation:
Answer
  • Use of plants (phytoremediation) or microorganisms to clean up contaminated agricultural soil
  • e.g., Sunflower to remove heavy metals; bacteria to degrade pesticide residues

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Frequently Asked Questions

Recombinant DNA technology (genetic engineering) involves the isolation of a specific gene from one organism, inserting it into a vector (usually a plasmid), introducing the recombinant vector into a host organism (bacteria, yeast, etc.), and allowing the host to produce the desired protein. Applications include insulin production, GM crops, and gene therapy.