Everything you need to know about transgenic breeding !
Q. 1. What is transgenic?
Ans. Genetically engineered organisms are called transgenics. In other words, a genotype developed by the process of genetic engineering is called transgenic (plural transgenics). It may be a plant, an animal or microbes such as fungi, viruses and bacteria.
Q. 2. Who coined the term transgenic?
Ans. The term transgenic was first used in 1981 by Gordon and Ruddle.
Q. 3. In which crop first transgenic plant was developed?
Ans. The first transgenic plant was developed in tobacco in USA by Fraley et al in 1983.
Q. 4. How transgenic plants are developed?
Ans. Transgenic plants are developed by the techniques of genetic engineering. The sexual process is bypassed in developing transgenic plants.
Q. 5. What is transgene?
Ans. Transgene refers to foreign gene or modified gene of the same species which is used for development of transgenic organisms. Transgene may be from the same species (in modified form), related wild species, unrelated species and microbes such as fungi, bacteria and viruses.
Q. 6. What are sources of transgenes?
Ans. The main sources of transgenes are same species, related wild species, unrelated species, micro-organism and animals.
Q. 7. What is genetic transformation?
Ans. The process of transfer, integration and expression of transgene in an organism is called genetic transformation.
Q. 8. What are main features of transgenic plants?
Ans. The main features of transgenic plants are given below:
(i) Transgenic plants contain transgene.
(ii) They are developed by the process of genetic engineering.
(iii) The sexual process is bypassed in developing transgenic plants.
(iv) The frequency of transgenic plants is extremely low (0.001%).
(v) Transgenic plants are developed to solve specific problem which cannot be tackled by conventional methods.
Q. 9. What is transgenic breeding?
Ans. Genetic improvement of crop plants, domestic animals and useful micro-organisms, through genetic engineering, in relation to their economic use for mankind is referred to as transgenic breeding.
Q. 10. What is transgenic plant breeding?
Ans. Transgenic plant breeding refers to genetic improvement of crop plants in relation to various economic characters useful for human beings, through genetic engineering.
Q. 11. What are advantages of transgenic crop breeding?
Ans. The main advantages of transgenic plant breeding are briefly presented below:
(i) It is a rapid method of crop improvement.
(ii) It overcomes barriers of cross incompatibility.
(iii) It is useful in solving those problems which cannot be solved by conventional methods.
(iv) It permits gene transfer from any source including animals.
Q. 12. What are methods of foreign gene transfer?
Ans. There are four important methods of foreign gene transfer as given below:
(i) Plasmid method or biological method
(ii) Particle bombardment method
(iii) Direct DNA uptake method
(iv) Micro-injection method.
Q. 13. What is plasmid?
Ans. Plasmids are extra chromosomal elements which are found in bacterial cell. They can replicate independently of chromosomal DNA and are not essential for normal growth and function of a bacterium. Plasmids are used as cloning vectors in genetic engineering. The soil bone bacterium Agrobacterium tumefaciens is used for development of transgenic plants.
Q. 14. What is biological method of DNA delivery?
Ans. The plasmid method is also known as biological method of DNA delivery. In this method, Agrobacterium tumefaciens is used for gene transfer.
This method of foreign gene transfer consists of following four main steps:
(i) Gene cloning through plasmids of Agrobacterium tumefacirens.
(ii) Mixing of cloned genes with cell or protoplast culture for transformation.
(iii) Identification of transformed cells by screening in culture medium containing Kanamycin. In kanamycin medium only transformed cells will survive and rest will die,
(iv) Regeneration of transformed cells into whole plant.
Q. 15. What are advantages of plasmid method of DNA delivery?
Ans. There are two main advantages of Agrobacterium mediated DNA transfer method as given below:
(i) This method has same control over the copy number and site of integration of transgenes which is not possible in particle bombardment method.
(ii) This is cheaper method of foreign gene transfer than particle bombardment method.
Q. 16. What are limitations of plasmid method of genetic transformation?
Ans. There are three main limitations of plasmid method of foreign gene transfer as follows:
(i) It has host specificity. It cannot infect monocotyledonous crops especially cereals.
(ii) The somaclonal variation is very high which poses problems in identification of transformed cells.
(iii) The regeneration of cells or protoplast into whole plant is very slow.
Q. 17. What is particle bombardment method of DNA delivery?
Ans. In this method, foreign DNA is delivered into plant cells through high velocity metal particles. This method is also known as biolistic micro-projectile bombardment, microballestics and particle acceleration method.
Q. 18. Which plant material is used for particle gun method?
Ans. In this method, re-generable tissues or organs are required for bombardment. Generally, meristems, immature embryos, embryogenic callus and suspension culture have been used for DNA delivery in different crop plants. Isolation of protoplast is not essential in this method.
Q. 19. What are the metals used for particle bombardment?
Ans. Generally, gold and tungsten particles are used for bombardment. These metals do not react with plant tissues. Gold particles, being dense, can penetrate into deeper cell layers than tungsten particles. These two metals are commonly used for bombardment because they do not react with DNA and their fine particles can be made.
Q. 20. How DNA is delivered through particle gun?
Ans. Minute particles (1.0-1.5 µ m) of tungsten or gold are coated with DNA of interest. The primary cloned form of DNA i.e. plasmid construction is used for coating with gold or tungsten particles. The DNA coated particles are accelerated with such force that they should penetrate the outer cell wall of target tissues. Some of the DNA of these particles enters in the nuclei of target cells and is integrated with the DNA of host cells resulting in transformation.
Q. 21. What are types of particle gun?
Ans. The particle gun is of two types as follows:
(i) Gun powder driven device, and
(ii) Helium particle inflow gun.
The gun powder device is more cumbersome as it requires more DNA loaded particles than helium particle inflow gun. Hence, the helium particle inflow gun is in more common use than gun powder device.
Q. 22. Name the crops in which particle acceleration method has been used for genetic transformation.
Ans. Particle acceleration method has been used for development of transgenic plants in several crops such as wheat, barley, oats, rice, corn, sugarcane, cotton, peanut, soybean, common bean, papaya, sunflower, tobacco, etc.
Q. 23. What are advantages of particle gun method of DNA delivery?
Ans. There are two main advantages of particle gun method of genetic transformation as follows:
(i) This method does not exhibit host specificity, it can be effectively used for development of transgenic plants in monocots as well as dicots.
(ii) This method is technically simpler than Agrobacterium method. Various plant parts such as meristems, embryos and leaves can be used for bombardment.
Q. 24. What are disadvantages of particle gun method?
Ans. This method has following two main disadvantages:
(i) There is no control over the copy number and site of integration of foreign gene.
(ii) The equipment is very costly which prohibits its use by many researchers.
Q. 25. Explain direct DNA transfer method of genetic transformation.
Ans. This method is used with protoplast. A suspension of protoplast with desired DNA is prepared. Then high voltage current is applied to the protoplast-DNA suspension. The electric current leads to formation of small temporary holes in the membrane of protoplasts through which the DNA can pass. After entry into the cells, the foreign DNA gets incorporated with the host genome resulting in genetic transformation.
Q. 26. What are limitations of direct DNA transfer method of genetic transformation?
Ans. This method can be used only in those crop species in which regeneration from protoplasts is possible. This method has been used in rice and corn.
Q. 27. What is micro-injection method of foreign gene transfer?
Ans. In this method, foreign DNA is delivered in the protoplasts through microscopic needles called micro-injections. This method does not have host range limitations. However, in this method also regeneration from protoplasts is a basic requirement which restricts application of this method only to those species that can regenerate from protoplasts.
Q. 28. What are the characters that have been improved through transgenic breeding?
Ans. In field crops, the following characters have been improved through transgenic breeding:
(i) Resistance to disease and insects
(ii) Resistance to herbicides
(iii) Resistance to drought conditions
(iv) Resistance to metal toxicity
(v) Quality of useful products
(vi) Development of male sterility.
Q. 29. Cite examples of transgenic insect resistance in crop plants.
Ans. Examples of transgenic insect resistance in crop plants are given below:
(i) In cotton, resistance to Helicoverva has been transferred from soil borne bacterium Bacillus thuringiensis by Monsanto Company in USA.
(ii) In corn, resistance to European corn borer had been transferred from above bacterium.
(iii) In tobacco, insect resistance has been achieved by transferring trypsin inhibitor gene from cow pea.
Q. 30. Cite examples of transgenic disease resistance in crop plants.
Ans. Transgenic virus resistant genotypes have been developed in various crops such as tobacco, tomato, potato and cucumbers.
Q. 31. Cite examples of cold resistance achieved through transgenic breeding.
Ans. Examples of cold resistance achieved through transgenic breeding are cited below:
(i) In tomato and tobacco, anti-freezing gene has been transferred from fish (winter flounder).
(ii) In tobacco, cold resistance has been achieved by transferring a gene from Arabidopsis thaliana.
Q. 32. Cite example of male sterility induced through transgenic breeding.
Ans. In rapeseed, male sterility has been induced by transferring a gene from Bacillus amyloliquefaciens.
Q. 33. Cite examples of quality improvement achieved through transgenic breeding in crop plants.
Ans. Examples of quality improvement achieved through transgenic breeding are cited below:
(i) In potato, protein quality has been improved by transferring serum albumin gene from human,
(ii) In tobacco, protein quality has been improved by transferring glutelins gene of wheat.
(iii) In alfalfa, protein quality has been enhanced by transferring ovalbumin gene from chicken.
Q. 34. Cite examples of herbicide resistance in crop plants achieved through transgenic breeding.
Ans. Herbicide resistant transgenic plants have been developed in several crops such as cotton, tobacco, wheat, maize, potato, tomato, soybean, flax, rapeseed, sugar beet, alfalfa, cabbage and other crops. In majority of cases, herbicide resistant genes have been transferred from micro-organisms.
Q. 35. What are limitations of transgenic breeding?
Ans. The main limitations of transgenic breeding are given below:
(i) Transgenic plants sometimes exhibit unstable performance for the character under consideration.
(ii) Sometimes, the transgene has undesirable side effects.
(iii) The position of integration of foreign gene in the host genome affects the expression of transgene in the host plant.
(iv) The frequency of desirable transgenic is extremely row.
(v) Transgenic breeding is very expensive method of crop improvement. Moreover, development of transgenic plants requires high technical skill.
Q. 36. What is transgenic technology?
Ans. The technique or process of developing transgenic individuals is referred to as transgenic technology. It enables plant breeders to combine useful genes in one controlling specific characteristics in one kind of organism, and transferring these genes into another quite different organism, which will then also have those characteristics.
Q. 37. Define transformation technology?
Ans. The transfer of a gene from one organism and incorporation into the genome of other organism/individual by gene technology is called transformation and a cell containing foreign gene is called trans formant. Transformation technology leads to development of transgenic individuals and conveys the same meaning as transgenic technology.
Q. 38. What is genetic engineering?
Ans. Genetic engineering is the process of removing, modifying or adding desirable genes into the recipient cell or into the DNA strand of recipient plant by molecular techniques. It also has the same meaning as gene technology.
Q. 39. What is recombinant DNA technology?
Ans. Recombinant DNA is a hybrid or chimeric DNA which cam combines with DNA of any organism. Recombinant DNA technology refer to a set of techniques that are used to isolate the DNA from one organism, modify it and incorporate into the genome of another individual or organism. It is the same as genetic engineering.
Q. 40. What is genetic modification?
Ans. Genetic modification refers to transferring single gene between different plants and animals, turning existing genes up (switch on) and down (switch off), or removing a gene from its original position and placing it in a new position in the same organism. It also means the same as genetic engineering.
Q. 41. Compare transgenic and conventional breeding methods.
Ans. Comparison of transgenic and conventional breeding methods in presented below in Table 23.1:
Q. 42. Compare different methods of foreign gene transfer.
Ans. Comparison of methods of foreign gene transfer (DNA delivery) is presented below in Table 23.2: