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The answer is (a) Plasmid

The answer is (a) Bacteria

The answer is (b) Bacteriophage

The answer is (c) Restriction Endonuclease

Segments of DNA or RNA with the help of which C-DNA or RNA segments of some organism can be identified are called molecular probes. 

The molecular probes are of following types: 

• DNA probes
• RNA probes

In recombinant DNA technology, in order to introduce the desired gene in the targeted plant/animal, a carrier is required which can carry the desired gene and can enter the targeted plant/animal and replicate it’s DNA. This carrier is called a vector. Plasmids, Bacteriophages and Cosmids are used as a vector in recombinant DNA technology.

Various effective measures required to incorporate changes in the DNA make up of any organism is called recombinant DNA technology.

The enzyme which cut the DNA molecule at specific sites is called restriction endonuclease. These enzymes are just like molecular scissors, which cut DNA into the segment at specific sites.

When the desired gene is incorporated with the vector, several unwanted products are also obtained. In order to eliminate these unwanted products and to identify the recombinant DNA in the host cell, a special type of gene is used. This produces special features in the modified/transformed cells. This gene which is incorporated in the vector DNA is called a marker gene. Example: Kanamycin resistant gene.

Cosmids are a hybrid of plasmid and 2 (Lambda) phage. Such plasmids, in which DNA sequence of ‘Cos’ site of λ (Lambda) phage are inserted, are known as cosmids.

Collection of the cloned segments of the entire genome of any organism is called the genomic library. A genomic library is formed by taking out complete DNA content of the haploid set of chromosomes of an organism.

Besides marker genes, there are certain genes which produce or present some specific features in the host cell. These are called reporter genes. These genes produce a special effect on account of which the cells containing these genes look different from other cells. Example: LUC gene found in fire-fly (“Jugnoo”) and produces bioluminescence.

1. Southern Blotting technique: This technique is used for the analysis of DNA segments. This was developed by E.M. Southern (1975) and hence named so. In this technique, the DNA segments are transferred on a nitrocellulose filter. These are then identified by hybridization with the DNA probes. 

2. DNA Fingerprinting: DNA Finger Printing was discovered by Alec Jeffreys and coworkers (1985). In this method DNA of a specific person is cut into small segments and is separated in the form of bands by electrophoresis. The identity of a person can be established by the specific base sequence found in the DNA of the person. This technique is used in resolving disputed paternity of any child and in detecting genetic diseases prior to the birth of a child. It is also used in the identification of criminals (Murderers and Rapists etc.) 

3. Polymerase Chain Reaction (PCR): Polymerase Chain Reaction was discovered by Mullis (1989). It is a powerful technique by which millions of copies of one DNA molecule can be obtained in a very short time without involving vectors for replication of DNA. This is performed in DNA thermal cycler. By repeating this cycle 20 – 30 times lacs of copies of DNA are obtained. 

4. Nomenclature of Restriction Enzymes: 

• The first alphabet of the name of enzyme represents the name of the genus from which it has been isolated. It is written in capital letters.
• The two alphabets after this represent the species of the genus. These are written in small letters. Note: All the three letters are written in italics. Example: E co = Escherichia coli.
• The fourth alphabet (word) represents the strain of the species from which the enzyme has been isolated. Example Eco R = R strain of E.coli.
• If more than one restriction enzymes are derived from the same organism (same strain), these are indicated by Roman numbers. Example: Eco RI, First restriction enzyme from R strain of E.coli. Eco RII, Second restriction enzyme from R strain of E.coli. 

5. Features of Vectors: 

• It can be inserted easily into the host cell and can be isolated easily.  It should freely self replicate in the host cell.
• The vector must posses Restriction sites so that restriction enzyme can cut the DNA at that site so that the desired DNA fragment can be incorporated easily.
• It should have one marker gene or marker site which can help in the selection of recombinants cells. 
• Transformation should be easy and perfect. 
• For expression of desired foreign DNA, the vector should essentially possess components such as a promoter, operator regulating sites.

After isolation of the desired gene(s), a vector is required which can incorporate this gene and along with it enter in the host cell & replicate it’s DNA in it. This vector is called cloning vector. Plasmid, Bacteriophages and Cosmids are main cloning vectors used in recombinant DNA technology. 

Plasmids: 

• These are extrachromosomal components in the bacterial cell.
• The DNA is a circular and double-stranded molecule. 
• They contain an origin of replication site and can replicate independently of a bacterial chromosome. 
• They have specific restriction sites where the desired gene can be incorporated. 
• They have marker sites. 
• The plasmid may contain 3 to one thousand genes. 

Bacteriophage: 

• The viruses which infect bacterially and cause lysis of bacterial cell are called bacteriophages. Example: λ (Lambda) phage and M₁₃ phage etc. 
• Bacteriophages are a better vector as compared to plasmids. 
• Large DNA segments (24 Kbp) can be cloned in the bacteriophages.
• Each bacteriophage produces a plaque in the culture. Hence their identification is easy. 

Cosmid:

• This is a hybrid of plasmid and λ (Lambda) phage.
• These can replicate in the host cell just like a plasmid.
• Due to the presence of ‘Cos’ site, these are packed like phage particles.
• Cosmids can be used to clone the DNA segment of up to 45 Kbp.

Restriction Fragment Length Polymorphism is abbreviated as RFLP.

Molecular Probes: 

Segments of DNA or RNA with the help of which cDNA or RNA segments of any organism present in it can be identified are called molecular probes. 

The molecular probes are of two types. 

• DNA probes. 
• RNA probes. 

Importance of Probes: 

• These are used to identify specific DNA segments used in the research of genetic engineering.
• Pollutants in food can be detected with the help of probes.
• These are used in the field of forensic science, in resolving disputed paternity issues and establishing the family relationship.
• These can be used to identify an improved variety of crops and hybridized seeds of crops.

Scientist working in the field of biotechnology have succeeded in achieving results which have proved advantageous in the field of medical science, agriculture and industries. By using these techniques it has become possible to improve the variety of agricultural crops and domestic animals and also the quality of industrial products. Presently biotechnology is considered as the most important branch of biology. 

Some important achievements are as follows: 

• Cloning of Nitrogen fixation (Nif) gene in cereal crops. 
• Cloning of Haemophilic gene.
• Cloning of Hepatitis B virus gene. 
• Cloning of Human growth hormone and insulin gene.
• Cloning of penicillin G acylase gene for production of penicillin
• Work on the Human genome project.