Biotechnology

Step 1: Understanding the Concept:
The question describes a genetic engineering experiment to enhance the production of mugineic acid in rice. It specifically mentions the introduction of two genes abbreviated as {naat-A} and {naat-B} and asks for the name of the enzyme they encode.
Step 2: Key Formula or Approach:
The key to solving this question lies in understanding the nomenclature used in molecular biology and biochemistry. The gene name often directly corresponds to the enzyme it encodes. Here, the gene is named {naat}. We need to identify the enzyme name that corresponds to this abbreviation.
Step 3: Detailed Explanation:
Let's break down the biosynthesis pathway for mugineic acids (a type of phytosiderophore): The enzymes involved are:

NAS: Nicotianamine Synthase
NAAT: Nicotianamine Aminotransferase
DMAS: Deoxymugineic Acid Synthase
The question explicitly states that the introduced genes are {naat-A} and {naat-B}. The abbreviation {naat} directly stands for Nicotianamine Aminotransferase. Therefore, these genes encode the subunits of the enzyme Nicotinamine aminotransferase.
Step 4: Final Answer:
The genes {naat-A} and {naat-B} encode the enzyme Nicotinamine aminotransferase.

Step 1: Understanding the Concept:
This question describes blue-white screening, a common technique used in molecular cloning to identify bacteria that have taken up a recombinant plasmid (a plasmid containing an inserted piece of foreign DNA). The technique relies on the principle of insertional inactivation.
Step 2: Detailed Explanation:
Let's break down the components:

lac-Z gene: This gene codes for the enzyme -galactosidase.
X-gal: A colorless artificial substrate for -galactosidase. When cleaved by the enzyme, it produces a blue-colored product.
IPTG: An inducer of the lac operon, which ensures that the lac-Z gene is expressed.
Multiple Cloning Site (MCS): A short region containing many unique restriction sites, placed intentionally inside the lac-Z gene.
Now let's consider the two possible outcomes for transformed cells (cells that have taken up a plasmid):

Non-recombinant plasmid: The plasmid has re-ligated without an insert. The lac-Z gene is intact. The bacteria will produce functional -galactosidase. This enzyme will cleave X-gal, and the bacterial colony will turn blue.
Recombinant plasmid: A piece of foreign DNA has been successfully inserted into the MCS. This insertion disrupts the lac-Z gene (insertional inactivation). The bacteria cannot produce functional -galactosidase. As a result, X-gal is not cleaved, and the bacterial colony remains its natural color, which is white.
Non-transformed cells (cells that did not take up any plasmid) will not grow at all if the plasmid also contains an antibiotic resistance gene and the medium contains that antibiotic (which is standard practice). If they were to grow, they would be white as they lack the lac-Z gene.
Step 3: Final Answer:
Transformed cells containing the recombinant plasmid have an inactivated lac-Z gene and therefore will appear white on the X-gal/IPTG medium.

Step 1: Understanding the Concept:
The question asks for the correct chronological order of the major steps involved in cryopreservation, which is the process of preserving biological material (like plant cells) by cooling it to very low temperatures, typically in liquid nitrogen ( C).
Step 2: Detailed Explanation:
Let's analyze the logical flow of the process:

A. Raising sterile tissue culture: First, you need the biological material to preserve. You start by growing a healthy, sterile, and actively dividing culture of the plant cells or tissues. This is the starting material.
D. Addition of cryoprotectants: Before freezing, you must treat the cells with cryoprotectants (e.g., DMSO, glycerol). These substances protect the cells from damage caused by ice crystal formation during the freezing process. This is a crucial pre-treatment step.
C. Freezing, Storage: After adding cryoprotectants, the cells are subjected to a controlled cooling protocol to freeze them, and then they are transferred to long-term storage in liquid nitrogen.
B. Determination of viability: After a period of storage, and especially when you need to use the material, the cells are thawed. It is then essential to test their viability (i.e., to check if they have survived the freezing and thawing process) using methods like staining (e.g., with TTC or fluorescein diacetate). This is the final quality-control step.
Step 3: Final Answer:
The correct sequence of steps is: Raise the culture (A), add protective chemicals (D), freeze and store it (C), and finally, check if it survived (B). This corresponds to the order A, D, C, B.

Step 1: Understanding the Concept:
The question asks for a key characteristic of a Bacterial Artificial Chromosome (BAC) vector. BACs are cloning vectors used in molecular biology.
Step 2: Detailed Explanation:
Let's analyze the features of BAC vectors:

BACs are based on the F-plasmid (fertility plasmid) of {E. coli}.
Their most important feature is their ability to accept and maintain very large DNA inserts, typically ranging from 150 to 350 kilobase pairs (kbp). This makes them invaluable for constructing genomic libraries and for sequencing entire genomes.
They use bacterial cells (specifically {E. coli}) as hosts, as indicated by the name "Bacterial" Artificial Chromosome.
They contain essential vector components, including an origin of replication (oriS from the F-plasmid) that allows them to replicate autonomously in the host cell. The F-plasmid origin maintains a very low copy number (1-2 copies per cell), which contributes to the stability of large inserts.
They possess selectable markers, such as an antibiotic resistance gene (e.g., chloramphenicol resistance), to allow for the selection of host cells that have successfully taken up the vector.
Evaluating the options:

(A) They can carry large DNA inserts: This is the primary and defining characteristic of BACs.
(B) They use eukaryotic cells as hosts: This is incorrect. They use bacterial hosts. Yeast Artificial Chromosomes (YACs) use eukaryotic (yeast) hosts.
(C) They lack selectable markers: This is incorrect. They must have selectable markers for cloning to be feasible.
(D) They do not replicate autonomously: This is incorrect. They have an origin of replication and replicate along with the host cell's chromosome.
Step 3: Final Answer:
The most significant characteristic feature of a BAC vector is its capacity to carry large DNA inserts.

Step 1: Understanding the Concept:
The question asks to identify which of the listed molecular marker techniques rely on the Polymerase Chain Reaction (PCR) as a core part of their methodology. PCR is a technique used to amplify specific segments of DNA.
Step 2: Detailed Explanation:
Let's examine each marker technique:

A. Restriction Fragment Length Polymorphism (RFLP): This is a non-PCR based technique. It involves cutting genomic DNA with restriction enzymes, separating the resulting fragments by gel electrophoresis, and then using a labeled probe to detect specific fragments via Southern blotting. No amplification step is involved.

B. Random Amplified Polymorphic DNAs (RAPD): The name itself says "Amplified". This technique uses short, arbitrary primers to amplify random segments of the genomic DNA using PCR. The presence or absence of amplified bands indicates polymorphism. PCR is essential.

C. Amplified Fragment Length Polymorphism (AFLP): This technique also has "Amplified" in its name. It is a multi-step process that begins with restriction digestion of DNA, followed by ligation of specific adapters, and then selective PCR amplification of a subset of these fragments. PCR is essential.

D. Sequence-Tagged Sites (STSs): An STS is a short, unique sequence in a genome. Its presence within a DNA sample is detected by designing specific primers for that sequence and performing a PCR assay. A successful amplification (producing a band of the expected size) confirms the presence of the STS. PCR is essential.

Step 3: Final Answer:
Based on the analysis, RAPD, AFLP, and STS are all PCR-based techniques, while RFLP is not. Therefore, the correct group is B, C, and D.

Step 1: Understanding the Concept:
The question asks for the logical and chronological sequence of steps required to create a genetically modified (GM) plant.
Step 2: Detailed Explanation:
Let's arrange the steps in a logical workflow:

B. Identification of a desired gene: The very first step is to identify a gene that confers a desirable trait (e.g., insect resistance, herbicide tolerance, improved nutrition). You must know what gene you want to transfer before you can do anything else.
A. Insertion of the gene into the vector: Once the desired gene is isolated, it needs to be inserted into a suitable carrier, or vector (usually a plasmid like the Ti plasmid from {Agrobacterium tumefaciens}). This creates a recombinant DNA molecule.
D. Transfer of the vector into a plant cell: The recombinant vector is then used to transfer the desired gene into the target plant cells. This can be done using methods like {Agrobacterium}-mediated transformation or a gene gun.
C. Selection and screening of transformed plants: The transformation process is not 100\% efficient. Therefore, after transformation, it is crucial to select the cells that have successfully incorporated the new gene (often using selectable markers like antibiotic resistance) and then regenerate whole plants from these transformed cells. These plants must then be screened to confirm the presence and expression of the new gene and the desired trait.
Step 3: Final Answer:
The correct sequence of steps is: Identify the gene (B), put it in a vector (A), transfer the vector to the plant (D), and then select and screen the results (C). This corresponds to the order B, A, D, C.

Step 1: Understanding the Concept:
The question asks for the main purpose of incorporating the Bt toxin gene into crops such as cotton. "Bt" stands for {Bacillus thuringiensis}, a soil bacterium.
Step 2: Detailed Explanation:


The bacterium {Bacillus thuringiensis} naturally produces a class of proteins called Cry proteins, commonly known as Bt toxins.
These proteins are harmless to humans, mammals, and most beneficial insects, but they are highly toxic to the larvae of certain insect pests, such as the cotton bollworm.
The mechanism of action involves the insect larva ingesting the protein. In the alkaline environment of the insect's midgut, the inactive protoxin is cleaved into its active form. This active toxin then binds to specific receptors on the gut wall, creating pores that lead to cell lysis, gut paralysis, and ultimately, the death of the insect.
Genetic engineering has allowed scientists to isolate the gene (Cry gene) that codes for this toxin from the bacterium and insert it into the genome of plants like cotton, corn, and brinjal.
The resulting genetically modified (GM) crop, such as Bt Cotton, can produce its own Bt toxin. When a susceptible insect pest tries to feed on the plant, it ingests the toxin and is killed. Therefore, the primary function of the Bt toxin is to make the plant resistant to certain insect pests, effectively making it act as a natural insecticide.
Step 3: Final Answer:
The primary function of Bt toxin in GM crops is to act as a built-in, natural insecticide, protecting the plant from specific insect pests.

Concept: Some plants have the ability to survive extreme dehydration and revive upon rehydration. Such plants are called resurrection plants. In Pteridophytes, certain species show this remarkable adaptation.
Step 1: Understanding the term "resurrection plant".}
A resurrection plant can withstand prolonged dry conditions and resume normal metabolic activity when water becomes available again.
Step 2: Identifying the correct genus.}
Among Pteridophytes, Selaginella (especially Selaginella bryopteris) is well known for its ability to survive desiccation and revive after rehydration. Hence, it is called the resurrection plant.
Step 3: Eliminating other options.}

• Marsilea – An aquatic fern, does not show resurrection ability.
• Equisetum – Known as horsetail, lacks this property.
• Pteris – A typical fern, no resurrection feature.

Concept: Diatoms are unicellular algae belonging to Bacillariophyceae, known for their unique cell wall structure.
Step 1: Understanding diatom cell wall.}
The cell wall of diatoms is called a frustule, which is made up of two overlapping halves.
Step 2: Identifying composition.}
The frustule is primarily composed of silica (hydrated silicon dioxide), giving it a glass-like appearance.
Step 3: Eliminating other options.}

• Cellulose – Found in plant cell walls.
• Chitin – Found in fungi.
• Pectin – Present in plant cell walls.