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weeds.
(v) The DNA fragments separate (resolve) according to their size through sieving effect
provided by the agarose gel. The smaller the fragment size, the farther it moves.

(vi) The separated DNA fragments can be visualised only after staining the DNA with a
compound known as ethidium bromide followed by exposure to UV radiation.
(vii) The DNA fragments can be seen as bright orange coloured bands. These separated
bands are cut out from the agarose gel and extracted from the gel piece. This is called
elution.
(viii) The purified DNA fragments can be used in constructing recombinant DNA by joining
them with cloning vectors.
8. Cloning vectors are the DNA molecules that can carry a foreign DNA segment into the
host cell.
(i) The vectors used in recombinant DNA technology can be:
(a) Plasmids Autonomously replicating circular extra-chromosomal DNA.
(b) Bacteriophages Viruses infecting bacteria.
(c) Cosmids Hybrid vectors derived from plasmids which contain cos site of X phage.
(ii) Copy number can be defined as the number of copies of vectors present in a cell.
(iii) Bacteriophages have high number per cell, so their copy number is also high in genome.
(iv) Plasmids have only one or two copies per cell.
(v) Copy number can vary from 1-100 or more than 100 copies per cell.
(vi) If an alien piece of DNA is linked with bacteriophage or plasmid DNA, its number can be
multiplied equal to the copy number of the plasmid or bacteriophage.
(vii) Features Required to Facilitate Cloning into Vector
(a) Origin of replication (Ori) (b) Selectable marker
(c) Cloning sites (d) Vectors for cloning genes in plants and animals.
(a) Origin of replication (Ori) is a sequence from where replication starts.
• Any piece of DNA when linked to this sequence can be made to replicate within the host
cells.
The sequence is also responsible for controlling the copy number of the linked DNA.
(ii) Selectable marker helps in identifying and eliminating non-transformants and selectively
permitting the growth of the transformants.
• Transformation is a process through which a piece of DNA is introduced in a host
bacterium.
• The genes encoding resistance to antibiotics such as ampicillin, chloramphenicol,