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

Biotechnology is the use of living organisms, cells, or biological processes to develop products and technologies that benefit human beings.

Major branches:

• Red biotechnology — medical applications (pharmaceuticals, gene therapy, diagnostics)
• Green biotechnology — agricultural applications (GM crops, biopesticides, biofertilisers)
• White/Grey biotechnology — industrial and environmental applications (biofuels, bioremediation)
• Blue biotechnology — marine and aquatic applications

Applications:

• Production of insulin, growth hormone, vaccines by recombinant DNA technology
• GM crops with pest resistance, herbicide tolerance, improved nutrition (Golden rice)
• DNA fingerprinting for forensics and paternity testing
• Bioremediation of polluted environments
• Tissue culture for plant propagation
• PCR for disease diagnosis (COVID-19 test uses RT-PCR)

Recombinant DNA technology involves combining DNA from different organisms to create organisms with new, useful traits.

Tools required:

• Restriction endonucleases ("molecular scissors") — cut DNA at specific sequences
• DNA ligase ("molecular glue") — joins DNA fragments
• Vectors (plasmids, viruses) — carry foreign DNA into host cells

Steps:

1. Identification and isolation of the desired gene (e.g., human insulin gene)

2. Cutting — restriction enzyme cuts both the desired gene and the vector (plasmid) at the same recognition sequence, creating sticky ends

3. Ligation — DNA ligase joins the desired gene into the vector → recombinant DNA (rDNA)

4. Transformation — recombinant plasmid is introduced into a host cell (e.g., E. coli bacteria)

5. Cloning and expression — host cells multiply; the inserted gene is expressed; the desired protein (e.g., insulin) is produced in large amounts

6. Extraction and purification of the protein product

Example: Human insulin gene → inserted into E. coli → bacteria produce human insulin (Humulin) → used to treat diabetes

PCR is a laboratory technique to amplify (make millions of copies of) a specific DNA sequence in a short time.

Invented by: Kary Mullis (Nobel Prize 1993)

Components needed:

• Template DNA (DNA to be amplified)
• Primers (short DNA sequences complementary to the target region)
• DNA polymerase (Taq polymerase — heat stable, from Thermus aquaticus)
• dNTPs (building blocks of DNA)

Steps (each cycle takes ~2 minutes):

1. Denaturation (94°C): Heat separates the double-stranded DNA into single strands

2. Annealing (50–65°C): Primers bind (anneal) to their complementary sequences on each single strand

3. Extension (72°C): Taq polymerase synthesises new DNA strands using dNTPs, starting from the primers

Each cycle doubles the DNA: After 30 cycles → over 1 billion copies of the target sequence

Applications of PCR:

• Diagnosis of infectious diseases (TB, HIV, COVID-19)
• DNA fingerprinting in forensics
• Detection of genetic diseases
• Ancient DNA analysis (archaeology)
• Paternity testing

DNA fingerprinting (DNA profiling) is a technique to identify individuals based on unique patterns in their DNA.

Developed by: Alec Jeffreys (1984)

Basis: Every person's DNA contains unique repetitive sequences called VNTRs (Variable Number of Tandem Repeats) or STRs (Short Tandem Repeats) — except identical twins.

Steps: 1. DNA extracted from sample (blood, hair, saliva, semen) 2. DNA cut with restriction enzymes 3. Fragments separated by gel electrophoresis (smaller fragments travel farther) 4. Fragments transferred to membrane and exposed to radioactive probes 5. Pattern of bands on X-ray film = DNA fingerprint (unique to individual)

Applications:

• Forensic science: Matching suspect DNA to crime scene evidence
• Paternity testing: Confirming biological parentage
• Identification of disaster or accident victims
• Immigration disputes
• Wildlife conservation: Identifying individuals and poachers

Genetically Modified (GM) crops are plants whose DNA has been altered using genetic engineering to introduce new traits that do not occur naturally in the species.

Examples:

Controversies/Concerns:

• Unknown long-term health effects on humans
• Environmental impact — gene flow to wild relatives (superweeds)
• Loss of biodiversity
• Corporate control of seeds (monopoly by agribusinesses)
• Ethical concerns about "playing God"
• Lack of labelling in some countries

In India: Bt cotton (approved 2002) is widely grown. Bt brinjal was approved but kept on hold due to public concerns.

Cloning is the production of genetically identical copies of an organism using its somatic (body) cells.

Dolly the sheep (1996):

• First mammal cloned from an adult somatic cell
• Cloned by Ian Wilmut and colleagues at the Roslin Institute, Edinburgh, Scotland
• Technique: Somatic Cell Nuclear Transfer (SCNT)

Steps in cloning Dolly: 1. Enucleation — nucleus removed from an unfertilised egg cell (from a Scottish Blackface ewe — surrogate) 2. Donor nucleus — nucleus from a mammary gland cell of a 6-year-old Finn Dorset ewe (the "parent") was taken 3. Fusion — The donor nucleus was fused into the enucleated egg using an electric pulse 4. Activation — The fused cell was stimulated to divide 5. Embryo development — The embryo was implanted into the surrogate mother 6. Birth — Dolly was born in July 1996 — genetically identical to the Finn Dorset donor sheep

Significance: Proved that a fully differentiated adult cell nucleus could be reprogrammed to develop into a complete organism. Opened possibilities for therapeutic cloning and stem cell research.

Dolly's fate: She developed arthritis and a lung disease; was euthanised in 2003 at age 6 (normal sheep lifespan is 10–12 years).