Mohan's electronics blog



Genetic Drift

The genetic drift or allelic drift is the evolutionary process of change in the allele frequencies (or gene frequencies) of a population from one generation to the next due to the phenomena of probability in which purely chance events determine which alleles (variants of a gene) within a reproductive population will be carried forward while others disappear. Especially in the case of small populations, the statistical effect of sampling error during random sampling of certain alleles from the overall population may result in an allele, and the biological traits that it confers, to become more common or rare over successive generations, and result in evolutionary change over time.

The concept of Genetic drift was first introduced by Sewall Wright in the 1920s, and is now held to be one of the primary mechanisms of biological evolution. It is distinct from natural selection, a non-random evolutionary selection process in which the tendency of alleles to become more or less widespread in a population over time is due to the alleles' effects on adaptive and reproductive success.

Gene Pool

The gene pool is the complete set of unique alleles in a species or population. A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive. Meanwhile, low genetic diversity can cause reduced biological fitness and an increased chance of extinction. When all individuals in a population are identical with regard to a particular phenotypic trait they are known as Monomorphic.

Hardy-Weinberg Principle

Hardy-Weinberg principle states that when no evolution occurs in a population the allele and genotype frequencies do not change from one generation to the next. No evolution refers to no mutation, no gene flow, no natural selection, and no genetic drift. To be in equilibrium two more assumptions need to be made that random mating occurs and there are discrete, non-overlapping generations.

Speciation

Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages.Whether genetic drift is a minor or major contributor to speciation is the subject of much ongoing discussion. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are geographically isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry or laboratory experiments. Observed examples of each kind of speciation are provided throughout.

Agrobacterium tumefaciens

It has the ability to transfer and stably integrate foreign DNA into plant genome. Nif genes are tied to T1 plasmid and are allowed to integrate into genome of non-leguminous plants.

Azospirillum lipoferum

Nitrogen fixing bacteria present in the roots of Brazilian grasses and Maize. Scientists are trying to associate Azospirillum with cereals to reduce the use of chemical pesticides.

Penicillin

Antibiotic obtained from Penicillium notatum and Penicillium chrysogenum. Penicillin is a broad spectrum antibiotic. It prevents wall formation in bacteria and kills them.

Aspergillus niger

It is used in commercial preparation of citric acid from sugar beet and sugarcane molasses. It can convert 40% of sucrose to citric acid.

Alpha diversity

It is defined as the diversity of organisms sharing the same community or habitat. A combination of species richness and evenness is used to represent alpha diversity.

Bacillus thuringienesis

It is the soil bacterium produces a crystal protein called Cry protein in its spores which is toxic to larvae of certain insects. The gene encoding Cry protein is called cry gene and has been isolated and efforts are being made by scientists to transfer this gene into Chick pea and other pulses to protect them from severe damaged caused by insect pests.

Biopatency

Patency is a right given officially to an inventor to make or sell his/her invention and to prevent others from copying it. Countries like USA, Japan and European union award Biopatency for strains of microorganisms, cell lines, genetically modified plants and animals, DNA sequences, biotechnology products, procedures etc.

Biopiracy

It is the unauthorized use of patent resources by organizations and multinational companies of other nations. For example, the patent claimed by USA for the Basmati rice whose germplasm originally belong to India. The protein Brazzein from West African plant Pentadipiandra brazeana which is a low calorie sweetner has been patented in the USA.

Biowar

This involves the use of biological weapons against humans, crops and animals. Biological warfare involves bioweapon agents or toxins which attack humans, crops and animals and its use in war has been dated back to 5th century B.C. Bioweapon agents are contained in the containers and delivered as powders, sprays etc. Some of the potent pathogens used in biowarfare are Anthrax, Small pox, Botulinum pathogens.

Bioethics

It involves the set of standards that are used to regulate and monitor our activities in relation to biological world. Biotechnology has greatly exploited the biological world and there are several bioethical concerns which include over use, disrespect given to plants and animals and also the risk involved in the experiments.

Biological magnification

It is a trophic process in which retained substances become more concentrated with each link in the food chain.

Bioremediation

It is the use of microorganisms for the removal of pollutants.

Bottle neck effect

Genetic drift resulting from reduction of a population, typically by natural disaster, such that the surviving population is no longer genetically representative of the original population.

Competitive exclusion principle

The concept that when the populations of two species compete for the same limited resources, one population will use the resources more efficiently and have a reproductive advantage that will eventually lead to the elimination of the other population.

Transgenic organisms

Organisms that has become transformed following the introduction of new DNA into its genome is called transgenic organism. Transgenic crop plants contain a gene or genes which have been artificially inserted instead of plant acquiring them through pollination. The inserted gene sequence is called Transgene may come from another unrelated plant or from a completely different species. For example, Bt Corn with gene from Bacillus thuringienesis, resistant to over ripening of Tomato.

Transgenic animals have novel genes obtained from outside. For example, Plasminogen activator in milk (Goat). Transgenic microbes are being used in industry for producing different bio chemicals and various functions. For example, Pseudomonas putida has been changed by introducing Plasmids of different strains for Alcoholic fermentation.

Bt Cotton, a transgenic crop variety, has been introduced in India. The Bt cotton variety contains a foreign gene obtained from Bacillus thuringienesis. This bacterial gene, introduced genetically into the cotton seeds protects the plant from Bollworm, a major pest of cotton. Bt cotton requires only 2 sprays of pesticide while the normal variety requires 8 sprays. According to Indian Council of Agricultural Research (ICAR), India uses about half of its pesticides on cotton to fight against Bollworm menacle. Use of Bt cotton has led to a 3% - 27% increase in cotton yield in countries where it is grown

Gene transfer techniques

Used to transfer genes from one organism to another

1. Agrobacterium mediated gene transfer

2. Direct gene transfer using Biolistics gun, Electroporation, Microinjection etc.

Transgenic plants

The plants which carry additional stably integrated and expressed foreign genes transferred from other genetic sources are called as transgenic plants.

Agrobacterium mediated transfer

The most common techniques used to transfer genes to Dicotyledonous plants using Agrobacterium. Cereals are difficult to transform through Agrobacterium because they do not have the proper wound response, a necessary requirement for transformation.

Transgenic vegetables

First transgenic plant Flavr Savr- delayed ripening tomato – introduced by Calgene Inc.

USA in 1994.

Cherry, Endless summer (tomato) – contains Bt protein gene against fruit borer.

Freedom II Squash resistant to water melon mosaic virus

New leaf (Potato) resistant to Colorado beetle (Leptinotarsa decemlineata)

AmAl Amaranth

Parthenocarpy fruits Seed less fruits

Golden rice with high Vit. A content

Biological magnification

It is the process whereby certain substances such as pesticides or heavy metals move up the food chain, toxins build up a successive link of the food chain. It works their way into river or lakes and is eaten by aquatic organisms such as fish which in turn are eaten by large birds, animals or humans. The substance becomes concentrated in the chain. It is like a magnifying glass that makes things look bigger. Biological magnification makes toxin get bigger and stronger in the ecosystem.

Eg. 1 Some pesticides are considered as Environmental Estrogens. These chemicals interfere with sex hormones and cause decreases sperm counting, breast cancer, testicular cancer, mis carriage etc. Methoxyclor, Atrazine, Benomyl are examples.

Eg. 2 Beetals may have very low level of fat soluble pesticides, but the pesticides will build much greater levels till in a human that eats the beetal eating bird.

Eg. 3 DDT in food chain of coastal water of long island.

Pesticides

Organochlorides DDT, BHC, Aldrin, Endosulphan – These are lipophilic compounds accumulate In fat depots like liver.

Organophosphates Malathion, Parathion, Feritrothion- These affect nervous system.

Carbamates Carbaryl, Carbofuran - Inhibit Acetylcholine esterase.

Highly toxic pesticides DDT, BHC, Carbofuran, Aldrin

Well known pesticide Parathion

Insecticide for Malaria control Malathion

Furudan It is Carbofuran

Baygon It is Propoxus

Herbicides destroy the weeds by affecting the Photosystem II.

Pesticide Thread Mill More expensive and more poisonous pesticides used to obtain

target. Eg. Pesticides for Cotton in India.

Biopesticides

These are biological agents used to control pests. Devine and Colego first used Fungal spores in weed control.

Confusion technique of pest control uses Pheromones. It is used in IPM. Ecdysone,

JH etc are insect hormones used to control pests in IPM.

Pyrethrum is obtained from Chrysanthemum cinerariifolium is a natural plant insecticide. It is usedto make Mosquito coils.

Neem contains an Anti-feedant called Azadiraclitin.

Food crops

Barley, Cotton, Sorghum Ethiopia

Maize Mexico, Central America

Sunflower USA

Pineapple, Rubber Brazil

Tomato, Potato Aeruvian Andes

Orthodox seeds

These are seeds withstand low moisture and low temperature. Eg. Cereals, Legumes.

Recalcitrant seeds

These are seeds killed by drying and freezing. Eg. Jack fruit, Tea, Cocoa, Rubber, Palm.

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