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DNA FINGERPRINTING

DNA fingerprinting , also called DNA typing, DNA profiling, genetic fingerprinting, genotyping, or identity testing , in genetics method of isolating and identifying variable elements within the base-pair sequence of DNA (deoxyribonucleic acid). The technique was developed in 1984 by British geneticist Alec Jeffreys, after he noticed that certain sequences of highly variable DNA , which do not contribute to the functions of genes are repeated within genes. Jeffreys recognized that each individual has a unique pattern of minisatellites (the only exceptions being multiple individuals from a single zygote such as identical twins). DNA FINGERPRINTING

MESELSON AND STHAL EXPERIMENT

Meselson and Stahl’s Experiment Meselson and Stahl’s Experiment was an experimental proof for semiconservative DNA replication. In 1958, Matthew Meselson and Franklin Stahl conducted an experiment on E.coli which divides in 20 minutes, to study the replication of DNA. Experiment 15 N (heavy) and 14 N (normal) are two isotopes of nitrogen which can be distinguished based on their densities by centrifugation in cesium chloride (CsCl). Meselson and Stahl cultured E.coli in a medium constituting 15 NH 4 Cl over many generations. As a result, 15 N was integrated into the bacterial DNA. Later, they revised the 15 NH 4 Cl medium to normal 14 NH 4 Cl. At a regular interval of time, they took the sample and checked for the density of DNA. MESELSON AND STAHL INTERACTIVE MESELSON AND STHAL EXPERIMENT

DNA AS GENETIC MATERIAL

Frederick Griffith: Bacterial transformation In 1928, British bacteriologist Frederick Griffith conducted a series of experiments using Streptococcus pneumoniae bacteria and mice. Griffith wasn't trying to identify the genetic material, but rather, trying to develop a vaccine against pneumonia. In his experiments, Griffith used two related strains of bacteria, known as R and S. R strain. When grown in a petri dish, the R bacteria formed colonies, or clumps of related bacteria, that had well-defined edges and a rough appearance (hence the abbreviation "R"). The R bacteria were nonvirulent, meaning that they did not cause sickness when injected into a mouse. S strain. S bacteria formed colonies that were rounded and smooth (hence the abbreviation "S"). The smooth appearance was due to a polysaccharide, or sugar-based, coat produced by the bacteria. This coat protected the S bacteria from the mouse immune system, making them virulent (capable of ...

DNA REPLICATION

DNA REPLICATION: It is the process of producing two identical replicas of DNA from the original DNA molecule. This is the basis of inheritance. DNA replication is semiconservative . Each strand in the double helix acts as a template for synthesis of a new, complementary strand. New DNA is made by enzymes called DNA polymerases , which require a template and a primer (starter) and synthesize DNA in the 5' to 3' direction. During DNA replication, one new strand (the leading strand ) is made as a continuous piece. The other (the lagging strand ) is made in small pieces. DNA replication requires other enzymes in addition to DNA polymerase, including DNA primase , DNA helicase , DNA ligase , and topoisomerase . DNA REPLICATION DNA REPLICATION FORK ADDITION OF NUCLEOTIDES IN DNA REPLICATION DNA REPLICATION E.COLI

ICT AWARD

Common errors while writing Examination

Errors committed by children Remedial measures 1) Not going through the questions properly: Apart from 15 minutes browsing time, the students must go through the questions at least twice very carefully and with calm mind before attempting it. 2) Reaching the examination late which adds fuel to the already built up tension: Must reach the examination hall well in time and meditate for 2-3 minutes before browsing the question paper. 3) Not writing the question numbers correctly: Must be very careful in writing the question numbers. 4) All parts of an answer to a question are not written at one place: Should write all parts of a question at one place. In case if it is felt that some points couldn’t be recollected, leave some space and proceed to the next question and whenever recollected come back to it. 5) Presentation of answer not up to the mark and in a confused manner: Adequate practi...

STRUCTURE OF DNA

What is DNA? DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences. DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. ...

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