successfully due to adaptation in the polluted areas
of england. This evolution of dark, melanic variety of
moths, in response to industrial pollution is known as
industrial melanism.- (i) The property to generate a whole plant from any
cell/explant is called totipotency.
(ii) In case of asexually reproducing crops like banana, virus
infections spread rapidly. This is because the vegetative
propagules from virus-infected plants contain virus
particles. but the shoot apical meristems and some
young tissues surrounding them are often free from
viruses. Meristem culture, therefore, is often useful in
recovering virus-free plants from virus-infected plants
or clones. Meristem culture involves the development
of an already existing shoot meristem and later on the
regeneration of adventitious roots from the developed
shoots.
The explants commonly used in meristem culture are
shoot tips and nodal segments. These explants are
cultured on a medium containing a cytokinin (generally
baP). The plantlets thus obtained are subjected to
hardening and, ultimately, established in the field.
- (i) During secondary treatment, the effluent from
primary treatment is passed into large aeration tanks,
where it is agitated mechanically and air is pumped
into it. This allows vigorous growth of useful aerobic
microbes. The aerobic microbes consisting of micro-
algae (Chlorella pyrenoidosa), micro-fungi, bacteria and
protozoa, grow into “flocs”, and consume a major
part of organic matter, so that the bOD of sewage
is reduced. Now, the effluent is passed through a
sedimentation tank, where microbial flocs are allowed
to settle down. The settled material is called ‘activated
sludge’.
(ii) a small part of the activated sludge obtained in
settling tanks is pumped back into the aeration tank,
to serve as the inoculum. The remaining major part of
the activated sludge is pumped into large tanks called
anaerobic sludge digesters. The anaerobic bacteria digest
the organic mass, bacteria and fungi in the sludge.
During the process, they produce mixture of gases like,
methane, hydrogen sulphide and CO 2 , which constitute
biogas.
- (i) a = ampicillin resistance gene (ampr), d =
Tetracycline resistance gene (tetr).
(ii) The markers in pbr322 vector are antibiotic resistance
genes. Selection of recombinants due to inactivation of
antibiotics is a cumbersome procedure because it requires
simultaneous plating on two plates having different
antibiotics.
Therefore, alternative selectable markers have been
developed, like the coding sequence for b-galactosidase.
b-galactosidase metabolises a chromogenic substrate
X gal to produce a blue coloured precipitate which
gives blue colour to colonies. Cells containing a vector
carrying b-glactosidase coding sequence without DNa
insert give blue colonies while cells containing vectors
with a DNa insert within the b-galactosidase coding
sequence produce white coloured colonies and thus these
colonies are easily identified as recombinant colonies. This
is because, when a recombinant DNa is inserted within
the coding sequence of the enzyme b-galactosidase, it
results in inactivation of the enzyme, which is referred
to as insertional inactivation.- a bioreactor is a device, in which a substrate of low
economic value is utilised by living cells or enzymes to
generate a product of higher economic value. bioreactors
can be regarded as large sized vessels, in which large
volumes, 100 to 1000 litres, of raw materials, in culture
medium, are biologically converted into specific products,
individual enzymes etc. using microbial, plant, animal or
human cells. a bioreactor provides the optimal growth
conditions.
Growth conditions that a bioreactor provides for
obtaining the desired products are :
(i) Controlled environment for optimum product
yield
(ii) aseptic fermentation for a number of days and
prevention of escape of viable cells
(iii) adequate mixing and aeration for optimum growth
and production, without damaging the micro-
organism
(iv) easy and dependable temperature control
(v) facility of sampling - Plasmids are autonomously replicating circular extra-
chromosomal double stranded DNa. They are capable
of replicating within bacterial cells, independent of
the control of the chromosomal DNa. The plasmid
molecules may vary from 1-2 copies per cell to 15-100
copies per cell and even higher than this. If an alien