- In case of birds, the type of sex determination is ZW-ZZ
type. Female has two different sex chromosomes (AA + ZW)
whereas male has a pair of same chromosomes (AA + ZZ).
As the female has heteromorphic sex chromosomes, the
female is heterogametic and produces two types of eggs,
(A + Z) and (A + W). The male gametes or sperms are of
one type (A + Z). Therefore, in birds, sex is determined by
female. Chromosomal determination of sex in human beings
is of XX-XY type. Human beings have 22 pairs of autosomes
and one pair of sex chromosomes. The females possess two
homomorphic sex chromosomes, named XX while. The
males have two heteromorphic sex chromosomes, i.e., XY.
All the ova formed by female are similar in their chromosome
type (22 + X). Therefore, females are homogametic. The male
gametes or sperms produced by human males are of two types,
gynosperms (22 + X) and androsperms (22 + Y). Human
males are therefore, heterogametic. Thus, the genetic
makeup of the sperm determines the sex of the child in
case of human.
- Outbreeding is the breeding of the unrelated animals
which may be between individuals of the same breed,
but without a common ancestors for 4-6 generations, or
between different breeds or different species (interspecific
hybridisation).
Outcrossing is the mating of animals within the same breed
but having no common ancestors on either side of their
pedigree, up to 4–6 generations. The offspring of such a
cross is called as an outcross. It is the best breeding method
for animals that are below average in productivity in milk
production, growth rate in beef cattle, etc. Sometimes only
a single outcross helps to overcome inbreeding depression.
In crossbreeding, superior males of one breed are mated
with superior females of another breed. Many new animal
breeds have been developed by this strategy and it gives
better breeds. For example, cows of an inferior breed may
be mated to bulls of a superior breed to get better progeny.
Hisardale is a new breed of sheep developed in Punjab by
crossing Bikaneri ewes and Marino rams.
- (a) Chemical pesticides used in agricultural fields are toxic
and they kill even useful organisms along with harmful
ones, harm human beings and animals, pollute soil, water
and crop plants. It is estimated that despite the use of
chemical pesticides 30% of the agricultural produce is lost
to pathogens and pests because these continue to develop
resistance against various pesticides. Now, organic farmers
prefer biological control of diseases and pests to the use
of chemicals. Biopesticides are the biological agents that
control the growth of weeds, insects and pathogens in
an agricultural field. They have targeted actions and are
harmless to the crop plants, other beneficial field animals
and humans. In organic farming, pests and pathogens are
not eradicated but kept at manageable levels by a system of
checks and balances as operating in ecosystem. An organic
farmer holds the view that eradicating pests is undesirable
because without them the beneficial predatory and parasitic
organisms which depend upon them for food would also be
annihilated.
(b) Bacterium as a biocontrol agent : Bacillus thuringiensis is
effective against the cabbage looper.
Fungi as a biocontrol agent : Trichoderma found in root
ecosystem exerts biocontrol over several plant pathogens.
Insect as a biocontrol agent : Lady bird beetle and dragonflies
feeds on aphids and prey upon mosquitoes, respectively.
- (a) Small volume cultures cannot give large quantities of
the product. So, the large scale production (100-1000 litres)
of the products is carried out in bioreactors. Bioreactors are
vessels in which raw materials are biologically converted
into specific products by microbes, plants and animal cells
and their enzymes. It provides optimal growth conditions
such as temperature, pH, substrate, vitamins, oxygen and
salts. This type of culturing method produces a larger
biomass to get higher yields of desired proteins.
(b) The most commonly used bioreactor is stirred tank bioreactor.
It consists of a large stainless steel vessel with a capacity
of upto 500,000 dm^3 around which there is a jacket of
circulatory water used to control the temperature within
the bioreactor. An agitator with a series of flat blades
ensure thorough mixing of contents rotated with the help
of a motor so that nutrients come in close with the micro-
organisms. It also prevents setting out of the cells at the
bottom. Bioreactor also has adequate arrangement for
aeration, temperature and pH control. Sparger is a porous
ring at the bottom of the tank which aerates the culture.
There are a number of ports through which materials can be
introduced or withdrawn. A harvest line at the base of the
tank extracts the culture medium and microbial products. To
detect and regulate the pH and temperature changes, tank
is fitted with certain probes.
- (a) Restriction enzymes : These enzymes belongs to the
class of enzymes nucleases which breaks nucleic acids by
cleaving their phosphodiester bonds. They are of two types:
exonucleases and endonucleases. Exonucleases remove
nucleotides from the ends of DNA. The cutting of DNA at
specific locations within the DNA strand is possible with the
help of ‘molecular scissors’ called restriction endonuclease.
Restriction endonucleases make highly specific internal cuts
in the DNA strand. These enzymes recognise palindromic
sites within the DNA duplex and cut its strands by hydrolysing
the phosphodiester bonds. Their single stranded free ends
are called sticky ends which can be joined end to end by
DNA ligases. Restriction endonucleases serve as a tool for
cutting DNA molecules at predetermined sites, which is the
basic requirement for gene cloning or recombinant DNA
technology. For example, restriction endonuclease Eco RI
