GM Food - Benefits:
1. High yield without pest.
2. 70% reduction of pesticide usage.
3. Reduce soil pollution problem.
4. Conserve microbial population in soil.
Risks - believed to:
1. Affect liver, kidney function and cancer.
2. Hormonal imbalance and physical disorder.
3. Anaphylactic shock (sudden hypersensitive reaction) and allergies.
4. Adverse effect in immune system because of bacterial protein.
5. Loss of viability of seeds show in terminator seed technology of GM crops.

The advantages of Bt cotton are:
1. Yield of cotton is increased due to effective control of bollworms.
2. Reduction in insecticide use in the cultivation of Bt cotton
3. Potential reduction in the cost of cultivation.
Disadvantages
Bt cotton has some limitations:
1. Cost of Bt cotton seed is high.
2. Effectiveness up to 120 days after that efficiency is reduced.
3. Ineffective against sucking pests like jassids, aphids and whitefly.
4. Affects pollinating insects and thus yield.

Properties of Vectors:
1. Vectors are able to replicate autonomously to produce multiple copies of them along with their DNA insert in the host cell.
2. It should be small in size and of low molecular weight, less than 10 Kb (kilo base pair) in size so that entry/transfer into host cell is easy.
3. Vector must contain an origin of replication so that it can independently replicate within the host.
4. It should contain a suitable marker such as antibiotic resistance, to permit its detection in transformed host cell.
5. Vector should have unique target sites for integration with DNA insert and should have the ability to integrate with DNA insert it carries into the genome of the host cell. Most of the commonly used cloning vectors have more than one restriction site. These are Multiple Cloning Site (MCS) or polylinker. Presence of MCS facilitates the use of restriction enzyme of choice.

A restriction enzyme or restriction endonuclease is an enzyme that cleaves DNA into fragments at or near specific recognition sites within the molecule known as restriction sites.
Types
(i) Exonucleases - which remove nucleotides one at a time from the end of a DNA molecule. e.g. Bal 31, Exonuclease III.
(ii) Endonucleases - which break the internal phosphodiester bonds within a DNA molecule. e.g. Hind II, EcoRI, PvulI, BamHI, TaqI.
(iii) The restriction enzymes are called as molecular scissors
(iv) They are used in recombinant DNA technology as they recognize & cut DNA within a specific sequence.

(i) pBR 322 plasmid is a reconstructed plasmid and most widely used as cloning vector;
(ii) It contains 4361 base pairs. In pBR, p denotes plasmid, Band R respectively the names of scientist Boliver and Rodriguez who developed this plasmid.
(iii) The number 322 is the number of plasmid developed from their laboratory.
(iv) It contains amp^R and tet^R two different antibiotic resistance genes and recognition sites for several restriction enzymes.
(v) ori and antibiotic resistance genes. Rop codes for the proteins involved in the replication of the plasmid.

(i) ECORI is from Escherichia ( E ) coli (co), strain RY 13 (R) & first endonuclease (I) to be discovered.
(ii) It contains 2 different antibiotics resistance genes & recognition site for several restriction enzymes.
(iii) This sequence is referred to as a restriction site & is generally -palindromic which means that the sequence in both DNA strands at this site read same in 5' - 3' direction & in-the 3'-5' direction.

(iv) The exact kind of cleavage produced by a restriction enzyme is important in the design of a gene cloning experiment.
(v) Some cleave both strands of DNA through the centre resulting in blunt or flush end.
(vi) These are known as symmetric cuts.
(vii) Some enzymes cut in a way producing protruding & recessed ends known as sticky or cohesive end.
(viii) These are known as staggered or asymmetric cuts.