Genetics and Biotechnology
Category : UPSC
GENETICS AND BIOTECHNOLOGY
GENETICS
Heredity is the transmission of genetic characters from parent to off springs. Individuals of same species have some differences, these are called variation.
MENDEL’S FINDINGS
In all the seven traits that Mendel examined, one form appeared dominant over the other i.e., it marked the presence of the other allele, e.g.
BASIC TERMS USED IN INHERITANCE STUDIES · Allele: It is an alternative form of a gene which are located on same position (loci) on the homologous chromosome. Term allele was coined by Bateson. · Homozygous: A zygote is formed by fusion of two gametes having identical factors is called homozygote and organism developed from this zygote is called homozygous. Ex. TT, RR, tt. · Heterozygous: A zygote is formed by fusion of two different types of gamete carrying different factors is called heterozygote (Tt, Rr) and individual developed from such zygote is called heterozygous. · Hemizygous: If individual contains only one gene of a pair then individual is said to be hemizygous. Male individual is always hemizygous for sex linked gene. · Phenotype: It is the external and morphological appearances of an organism for a particular character. · Genotype: It is the genetic constitution or genetic make-up of an organism for a particular character. · Back cross: A back cross is a cross in which \[{{F}_{1}}\]individuals are crossed with any of their parents. · Test cross: When \[{{F}_{1}}\] progeny is crossed with recessive parent then it is called test cross. · Monohybrid test cross: The progeny obtained from the monohybrid test cross are in equal proportion, means 50% is dominant phenotypes and 50% is recessive phenotypes. It can be represented in symbolic forms as follows. \[{{F}_{1}}\]progeny (hybrid) \[\times \] Recessive parent
Monohybrid test cross ratio =1:1 · Dihybrid test cross: The progeny is obtained from dihybrid test cross are of four types and each of them is 25%. |
PARENTAL CROSS
Exceptions of Conclusions of Mendel
Exception of Dominance
There are two exceptions of law of dominance-
(i) Incomplete dominance
(ii) Co-dominance
LINKAGE
Sex Linkage
When the genes of vegetative/somatic characters are present on sex-chromosome, it is termed as sex linked gene and such phenomenon is known as sex-linkage.
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Sex linkage |
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X- linkage |
Y- linkage |
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Genes of somatic characters are found on X-chromosome. The inheritance of X-linked character may be through the males and females, e.g. Haemophilia, Colour blindness. |
The genes of somatic characters are located on Y- chromosome. The inheritance of such type of character occur only through the males, such type of character is called holandric character. These characters are found only in male. E.g.: Hypertrichosis (excessive hair on ear pinna.) |
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GENES
Genes are responsible for the characteristics features (or traits) of organism-plant or animals. The characteristics or traits of parents are transmitted to their progeny (off springs) through geneses present on their chromosomes during the process of sexual reproduction.
Lethal Gene
MULTIPLE ALLELE
Example of multiple allele
IA = dominant
IB = dominant
ID = recessive
Possible phenotypes - A, B, AB, O
Blood group |
Genotype |
Antigen or agglutinogen |
Antibody or agglutinin |
A |
\[{{I}^{A}}{{I}^{A}},{{I}^{A}}{{I}^{O}}\] |
A |
b |
B |
\[{{I}^{B}}{{I}^{B}},{{I}^{B}}{{I}^{O}}\] |
B |
a |
AB |
\[{{I}^{A}}{{I}^{B}}\] |
A & B |
None |
0 |
\[{{I}^{O}}{{I}^{O}}\] |
None |
A & b |
Possible genotype number =\[\underline{3\,\,(3\,\,\,\,\,1)}=6\,\,genotype\]
SEX DETERMINATION
Deoxyribose Nucleic Acid (DNA)
(i) Each DNA molecule consists of two polynucleotide chains.
(ii) The chains are helically coiled around a common axis.
(iii) DNA molecule has a diameter of 20 A are complete turn of helix is 3.4 A. So there are 10 bases per turn of helix.
(v) Each DNA chain is complementary chain to second chain.
Nucleoside = Deoxyribose + Nitrogenous base
Nucleotide = Deoxyribose + Nitrogenous base + Phosphate
GENETIC DISORDERS
(i) Haemophilia is an inherited disorder of blood in which essential clotting factor are either partly or completely missing.
(ii) In sickle-cell anaemia glutamic acid (glutamine) is replaced by valine at the sixth position in b chain of haemoglobin. It is a blood disease. Where the red blood blood cells become sickle shaped as compared to normal one.
BIOTECHNOLOGY
The Convention on Biological Diversity (CBD) defines biotechnology as any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use.
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Principles of Biotechnology |
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Genetic engineering |
Biochemical engineering |
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It is the manipulation of genes of an organism. Genetic engineering refers to artificial synthesis, isolation, modification, combination, addition and repair of the genetic material (DNA) to alter the phenotype of the host organism to suit human needs. |
These are the processes that help the growth of desired microbe/eukaryotic cell in large quantities in a sterile medium (Tissue culture technique) for the manufacture and multiplication of biotechnological product (antibiotics, vaccines, enzymes, medicines, hormones, etc.) |
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RECOMBINANT DNA TECHNOLOGY
Recombinant DNA technology, popularly known as ‘genetic engineering’ is a stream of biotechnology which deals with the manipulation of genetic material by man in vitro.
There are two distinct techniques/or introducing foreign genetic material into plant cell genome — indirect and direct transfer.
The first is indirect transfer through a vector which requires-
The second, through direct introduction of DNA, involves-
Thus, genetic engineering can be defined as the generation of new combination of heritable material by the insertion of desired genes or DNA of the cell, into any carrier system so as to allow their incorporation into a host organism in which they do not normally of cur but in which they are able to perform normal behaviour and propagation.
Basic Tools of Recombinant DNA Technology
Enzyme
A number of specific kind of enzymes are employed in genetic engineering. These include lysing enzymes, cleaving enzymes, synthesizing enzyme and joining enzymes.
They are further of 3 kinds—
(i) Exonucleases - which cut off nucleotides from 5’ or ‘3 ends of DNA molecule;
(ii) Restriction endonucleases — which cleave DNA duplex at specific points called restriction sites in such a way that single-stranded free ends project from each fragment of DNA duplex. These single-stranded free ends are called ‘sticky ends’ because they can join similar complementary ends of DNA fragment from some other source. Restriction endonuclease is called molecular scissors or a chemical scalpel.
3’- CTTAAG-5’ 5’-GAATTC – 3’
Vectors
High copy number, Presence of origin of replication (Ori), Presence of selectable marker, Presence of unique recognition site or cloning site and Ability to sustain in bacterial cell
Process of Recombinant Technology
Recombinant DNA (rDNA) is DNA created artificially by combining the DNA from two or more organisms into a single “recombinant” molecule. The term "recombinant DNA technology" also commonly known as 'DNA cloning,’ ‘molecular cloning' and 'gene cloning’, refers to the transfer of a segment of DNA from one organism to another organism (the “host cell”) where it reproduces.
Following are the steps in Recombinant DNA Technology
Step 1: Isolation of genetic material
At first required DNA sequence from the donor cell is identified. Later the required DNA is cut by the help of restriction enzymes at specific site, which result is single stranded sequence with “stick ends”.
Step 2: Cutting of DNA of specific locations
Second, cloning vectors from the host cell are identified and removed with the same restrictive enzyme applied to the donor DNA. Cloning vectors are DNA molecules in which another DNA fragment (i.e., foreign DNA) can be integrated and which are capable of independently replicating themselves and the foreign DNA once inserted into the host cell.
Step 3: Amplification of Gene of interest using PCR
PCR stands for Polymerase Chain Reaction. It is the process of amplifying a desired gene of interest into a number of copies. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase.
Step 4: Insertion of Recombinant DNA into the Host Cell/Organism
There are several methods of introducing the ligated DNA into recipient cells. Recipient cells after making them ‘competent’ to receive, take up DNA present in its surrounding. So, if a recombinant DNA bearing gene for resistance to an antibiotic (e.g. ampicillin) is transferred into E. coli cells, the host cells become transformed into ampicillin-resistant cells.
Step 5: Obtaining the Foreign Gene Product
After having cloned the gene of interest and having optimised the conditions to induce the expression of the target protein, one has to consider producing it on a large scale. If any protein encoding gene is expressed in a heterologous host, is called a recombinant protein.
APPLICATION OF BIOTECHNOLOGY
BT COTTON Bt means Bacillus thuringiensis. It is a gram positive dwelling bacterium. It produces crystal [Cry] protein. This Cry protein is toxic to larvae of certain insects. Each Cry protein is toxic to a different group of insects. The gene encoding cry protein is called cry gene. This Cry protein is isolated and transferred into several crops. A crop expressing a cry gene is usually resistant to the group of insects for which the concerned Cry protein is toxic. There are a number of them, for example, the proteins encoded by the genes cry IAc and cry lAb control the cotton bollworms, that of cry IAb controls corn borer. Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. The Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect. |
Problems related to GM foods are
Application of Biotechnology in Medicine
Genetically engineered insulin (humulin)
Transgenic Animals
(i) Transgenic animals can be specifically designed to allow the study of how genes are regulated and how they affect the normal functions of the body and its development, e.g., Information is obtained about the biological role of insulin like growth factor.
(ii) Transgenic animals are designed to increase our understanding of how genes contribute to the development of diseases; they are made to serve as models for human diseases.
(iii) Transgenic mice are being developed for use in testing the safety of vaccines, (e.g. polio vaccine). (iv) Transgenic animals with more sensitivity to toxic substances are being developed to test the toxicity of drugs.
Transgenic Plants
Transgenic Plants (of some species,) are easier to produce because plants have a lot oftotipotent tissue (meristem) that can be grown in culture and then induced to develop into a whole plant. One of the most common methods utilizes a natural gene transfer system called the Ti-plasmid of Agrobacterium tumefaciens which transfers a piece of DNA called T-DNA into the genome of infected plants.
Table: Transgenic plants
Transgenic plants |
Useful application |
Bt Cotton |
Pest resistance, herbicide tolerance and high yield. It is resistant to boll worm infestation. |
Flavr Savr Tomato |
Increased shelf-life (delayed ripening) and better nutrient quality. |
Golden rice |
Vitamin A-rich |
Potato |
Higher protein content |
Corn, Brinjal |
Insect resistance |
Soyabeen, Maize |
Herbicide resistance |
Ethical Issues
Bio piracy
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