GATE Biotechnology Plant, Animal and Microbial Biotechnology Syllabus

What is gametoclonal variation, and how does it differ from somaclonal variation?

Gametoclonal variation is the variation observed among plants regenerated from cultured gametic (haploid) cells such as microspores or pollen (e.g., via anther culture). It differs from somaclonal variation, which arises from somatic (diploid) tissue cultures.

What is a protoplast and how is it conventionally prepared?

A protoplast is a plant cell from which the cell wall has been completely removed, leaving only the plasma-membrane-bound cell. It is prepared enzymatically by digesting the wall with cellulase, hemicellulase, and pectinase in an osmotically stabilized (e.g., mannitol/sorbitol) medium.

Name two widely used methods of inducing protoplast fusion.

Chemical fusion using polyethylene glycol (PEG), often with high pH/high $\ce{Ca^2+}$; and electrofusion, where an electric field aligns protoplasts (dielectrophoresis) and a DC pulse fuses their membranes.

Distinguish a somatic hybrid from a cybrid.

A somatic hybrid contains the nuclear genomes of both parental protoplasts plus a mixture of their cytoplasms (mitochondria/chloroplasts). A cybrid (cytoplasmic hybrid) has the nucleus of only one parent but cytoplasm (organelles) from both parents.

What is the significance of producing cybrids in plant breeding?

Cybrids allow transfer of cytoplasmically (organelle) encoded traits, such as cytoplasmic male sterility (CMS) and certain herbicide or antibiotic resistances, into a desired nuclear background without altering the nuclear genome, useful for hybrid seed production.

Define a transgenic plant.

A transgenic (genetically modified) plant is one whose genome has been stably altered by the introduction and integration of one or more foreign genes (transgenes) using recombinant DNA / gene transfer techniques, with the trait heritable to progeny.

Classify gene transfer methods in plants into direct and indirect (vector-mediated) categories with examples.

Indirect (vector-mediated): Agrobacterium tumefaciens-mediated and plant viral vectors. Direct (vectorless): physical/chemical methods such as particle bombardment (biolistics), electroporation, microinjection, PEG-mediated DNA uptake, and silicon-carbide whisker method.

Describe the principle of Agrobacterium-mediated gene transfer.

Agrobacterium tumefaciens transfers a defined T-DNA segment of its Ti plasmid into the plant genome. In genetic engineering, the tumor genes are removed (disarmed) and the gene of interest plus a selectable marker are inserted between the T-DNA border sequences; vir genes mediate the transfer.

What are the T-DNA borders and the vir region, and what are their roles?

The T-DNA is flanked by 25-bp left and right border repeats that define the segment transferred to the plant. The vir (virulence) region of the Ti plasmid encodes proteins that process the T-DNA (nicking at borders) and mediate its transfer and integration into the plant genome.

Explain the biolistic (particle bombardment / gene gun) method.

DNA is precipitated onto micron-sized gold or tungsten particles, which are accelerated at high velocity (via helium pressure or gunpowder) to physically penetrate plant cells/tissues, delivering DNA into the cytoplasm and nucleus where it can integrate. It is the main method for monocots and chloroplast transformation.

What is electroporation and its application in plant transformation?

Electroporation applies brief high-voltage electrical pulses to create transient pores in the plasma membrane (usually of protoplasts), allowing exogenous DNA to enter the cell. It is a direct, vectorless transfer method useful where Agrobacterium is ineffective.

Define a selectable marker gene and give two common examples used in plants.

A selectable marker gene confers a trait (usually antibiotic or herbicide resistance) that allows transformed cells to survive on a selective medium while non-transformed cells die. Examples: nptII (neomycin phosphotransferase, kanamycin resistance) and hpt (hygromycin resistance); bar/pat (phosphinothricin/herbicide resistance).

What is a reporter gene and how does it differ from a selectable marker?

A reporter gene produces an easily assayable, visible/quantifiable product used to confirm gene expression and monitor transformation, but does not kill non-transformed cells. A selectable marker actively selects (allows survival of) transformed cells. Reporters indicate; markers select.

Name three common reporter genes and the assay/product of each.

GUS (uidA, β-glucuronidase) cleaves X-gluc giving a blue precipitate; GFP (green fluorescent protein) fluoresces green under UV/blue light without a substrate; luc (firefly luciferase) emits light with luciferin/ATP; lacZ (β-galactosidase) gives blue color with X-gal.

Why is the GUS reporter assay considered destructive while GFP is non-destructive?

The histochemical GUS assay requires incubation with the substrate X-gluc and usually killing/fixing the tissue to visualize the blue product. GFP fluoresces directly when illuminated, requiring no substrate or cofactor, so living tissue can be monitored repeatedly without damage.

What is micropropagation and what is its chief advantage?

Micropropagation is the rapid in vitro clonal multiplication of plants from small explants (shoot tips, nodes, meristems) through tissue culture. Its chief advantage is mass production of genetically uniform, disease-free plants in a small space irrespective of season.

Outline the standard stages of micropropagation.

Stage 0: selection/preparation of mother plant; Stage I: initiation and establishment of aseptic culture; Stage II: shoot multiplication; Stage III: rooting / shoot elongation; Stage IV: hardening and acclimatization (transfer to soil).

What is meristem culture primarily used for, and why does it work?

Meristem (meristem-tip) culture is used to produce virus-free plants. It works because the actively dividing apical meristem is largely free of viruses (viruses spread slowly through the vascular tissue that has not yet differentiated at the tip).

What is anther/microspore culture used to produce, and what is the ploidy of the resulting plants?

Anther (or isolated microspore) culture is used to produce haploid plants from pollen/microspores. Treatment with colchicine can double the chromosomes to give homozygous doubled haploids (diploids), valuable for rapidly fixing pure breeding lines.

What is somatic embryogenesis, and what is the role of 2,4-D in inducing it?

Somatic embryogenesis is the development of bipolar embryos from somatic cells. The auxin 2,4-D is commonly used to induce embryogenic competence/callus; its subsequent removal or reduction allows the proembryos to develop and mature into somatic embryos.

Why must auxin generally be removed for somatic embryos to mature?

High auxin (e.g., 2,4-D) maintains cells in a proliferative/embryogenic-induction state but inhibits the progression and maturation of embryos. Lowering or removing auxin releases this block, allowing the proembryogenic masses to develop polarity and mature into normal embryos.

What is animal cell culture, and distinguish anchorage-dependent from suspension cells.

Animal cell culture is the in vitro growth of cells from animal tissues. Anchorage-dependent cells require attachment to a solid surface to grow (most normal cells, fibroblasts); suspension (anchorage-independent) cells grow freely in liquid medium (e.g., blood-derived/lymphoid and many transformed cell lines).

Differentiate a primary culture, a cell line, and a continuous (immortal) cell line.

Primary culture: cells taken directly from tissue, finite lifespan. Cell line (finite): subcultured primary cells that proliferate for a limited number of passages then senesce. Continuous/established line: transformed or immortalized cells that divide indefinitely (e.g., HeLa, CHO).

What is the role of serum (e.g., fetal bovine serum) in animal cell culture media?

Serum supplies growth factors, hormones, attachment and spreading factors, transport proteins (e.g., transferrin, albumin), lipids, and minerals, and provides buffering/protease-inhibition. It promotes cell attachment, growth, and survival, though serum-free defined media are increasingly used for reproducibility.

How are hybridomas produced for monoclonal antibody (mAb) production?

An antigen-immunized animal's B-lymphocytes (antibody-producing but mortal) are fused with immortal myeloma cells (often using PEG). The resulting hybridomas are selected on HAT medium, then screened and cloned to obtain a single clone secreting a specific monoclonal antibody.

Explain the basis of HAT medium selection in hybridoma technology.

HAT (Hypoxanthine-Aminopterin-Thymidine) medium: aminopterin blocks de novo nucleotide synthesis, so cells must use the salvage pathway via HGPRT. Myeloma cells are HGPRT-deficient and die; unfused B cells die naturally. Only B-cell × myeloma hybridomas (HGPRT-positive and immortal) survive.

What is microbial biotechnology, and name two industrially important microbial products.

Microbial biotechnology uses microorganisms (bacteria, fungi, yeast) to produce useful products and processes. Examples: antibiotics (penicillin from Penicillium), enzymes (amylases, proteases), organic acids (citric acid from Aspergillus niger), ethanol (Saccharomyces cerevisiae), and recombinant proteins (insulin from E. coli).

Distinguish primary metabolites from secondary metabolites in microbial fermentation.

Primary metabolites are produced during the growth phase (trophophase) and are essential for growth (e.g., amino acids, ethanol, organic acids). Secondary metabolites are produced typically in the stationary phase (idiophase), are not essential for growth, and include antibiotics and pigments.

Compare batch, fed-batch, and continuous fermentation.

Batch: all nutrients added at start, nothing added/removed during run (closed). Fed-batch: substrate fed incrementally during the run to control growth/avoid substrate inhibition, no product withdrawal. Continuous: fresh medium added and culture withdrawn at equal rates to maintain steady state (open system).

Why is the auxin:cytokinin ratio described as quantitative rather than absolute in controlling morphogenesis?

Because it is the relative balance (ratio) of the two hormones, not their absolute concentrations, that directs the developmental fate; the same absolute auxin level can promote roots, shoots, or callus depending on the cytokinin level present, reflecting their antagonistic interactive control.