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Monthly Archives: April 2011

DNA FINGERPRINTING

DNA

DNA (Deoxyribonucleic acid) is a chemical structure that forms chromosomes. A piece of a chromosome that dictates a particular trait is called a gene.

Structurally, DNA is a double helix: two strands of genetic material spiraled around each other. Each strand contains a sequence of bases (also called nucleotides). A base is one of four chemicals (adenine, guanine, cytosine and thymine).

The two strands of DNA are connected at each base. Each base will only bond with one other base, as follows: Adenine (A) will only bond with thymine (T), and guanine (G) will only bond with cytosine (C).

What is DNA Fingerprinting?

The chemical structure of everyone’s DNA is the same. The only difference between people (or any animal) is the order of the base pairs. There are so many millions of base pairs in each person’s DNA that every person has a different sequence.

Using these sequences, every person could be identified solely by the sequence of their base pairs. However, because there are so many millions of base pairs, the task would be very time-consuming. Instead, scientists are able to use a shorter method, because of repeating patterns in DNA.

These patterns do not, however, give an individual “fingerprint,” but they are able to determine whether two DNA samples are from the same person, related people, or non-related people. Scientists use a small number of sequences of DNA that are known to vary among individuals a great deal, and analyze those to get a certain probability of a match.

Applications

1. Paternity and Maternity

Because a person inherits his or her VNTRs from his or her parents, VNTR patterns can be used to establish paternity and maternity. The patterns are so specific that a parental VNTR pattern can be reconstructed even if only the children’s VNTR patterns are known (the more children produced, the more reliable the reconstruction). Parent-child VNTR pattern analysis has been used to solve standard father-identification cases as well as more complicated cases of confirming legal nationality and, in instances of adoption, biological parenthood.

2. Criminal Identification and Forensics

DNA isolated from blood, hair, skin cells, or other genetic evidence left at the scene of a crime can be compared, through VNTR patterns, with the DNA of a criminal suspect to determine guilt or innocence. VNTR patterns are also useful in establishing the identity of a homicide victim, either from DNA found as evidence or from the body itself.

3. Personal Identification

The notion of using DNA fingerprints as a sort of genetic bar code to identify individuals has been discussed, but this is not likely to happen anytime in the foreseeable future. The technology required to isolate, keep on file, and then analyze millions of very specified VNTR patterns is both expensive and impractical. Social security numbers, picture ID, and other more mundane methods are much more likely to remain the prevalent ways to establish personal identification.

PROCESS

1. Isolating the DNA in question from the rest of the cellular material in the nucleus. This can be done either chemically, by using a detergent to wash the extra material from the DNA,or mechanically, by applying a large amount of pressure in order to “squeeze out” the DNA.

2. Cutting the DNA into several pieces of different sizes. This is done using one or more restriction enzymes.

3. Sorting the DNA pieces by size. The process by which the size separation, “size fractionation,” is done is called gel electrophoresis. The DNA is poured into a gel, such as agarose, and an electrical charge is applied to the gel, with the positive charge at the bottom and the negative charge at the top. Because DNA has a slightly negative charge, the pieces of DNA will be attracted towards the bottom of the gel; the smaller pieces, however, will be able to move more quickly and thus further towards the bottom than the larger pieces. The different-sized pieces of DNA will therefore be separated by size, with the smaller pieces towards the bottom and the larger pieces towards the top.

4. Denaturing the DNA, so that all of the DNA is rendered single-stranded. This can be done either by heating or chemically treating the DNA in the gel.

5. Blotting the DNA. The gel with the size-fractionated DNA is applied to a sheet of nitrocellulose paper, and then baked to permanently attach the DNA to the sheet. The Southern Blot is now ready to be analyzed.

In order to analyze a Southern Blot, a radioactive genetic probe is used in a hybridization reaction with the DNA in question. If an X-ray is taken of the Southern Blot after a radioactive probe has been allowed to bond with the denatured DNA on the paper, only the areas where the radioactive probe binds [red] will show up on the film. This allows researchers to identify, in a particular person’s DNA, the occurrence and frequency of the particular genetic pattern contained in the probe.

VNTRS

Every strand of DNA has pieces that contain genetic information which informs an organism’s development (exons) and pieces that, apparently, supply no relevant genetic information at all (introns). Although the introns may seem useless, it has been found that they contain repeated sequences of base pairs. These sequences, called Variable Number Tandem Repeats (VNTRs), can contain anywhere from twenty to one hundred base pairs.

Every human being has some VNTRs. To determine if a person has a particular VNTR, a Southern Blot is performed, and then the Southern Blot is probed, through a hybridization reaction, with a radioactive version of the VNTR in question. The pattern which results from this process is what is often referred to as a DNA fingerprint.

A given person’s VNTRs come from the genetic information donated by his or her parents; he or she could have VNTRs inherited from his or her mother or father, or a combination, but never a VNTR either of his or her parents do not have. Shown below are the VNTR patterns for Mrs. Nguyen [blue], Mr. Nguyen [yellow], and their four children: D1 (the Nguyens’ biological daughter), D2 (Mr. Nguyen’s step-daughter, child of Mrs. Nguyen and her former husband [red]), S1 (the Nguyens’ biological son), and S2 (the Nguyens’ adopted son, not biologically related [his parents are light and dark green]).

Because VNTR patterns are inherited genetically, a given person’s VNTR pattern is more or less unique. The more VNTR probes used to analyze a person’s VNTR pattern, the more distinctive and individualized that pattern, or DNA fingerprint, will be.

Problems In DNA Fingerprinting

Like nearly everything else in the scientific world, nothing about DNA fingerprinting is 100% assured. The term DNA fingerprint is, in one sense, a misnomer: it implies that, like a fingerprint, the VNTR pattern for a given person is utterly and completely unique to that person. Actually, all that a VNTR pattern can do is present a probability that the person in question is indeed the person to whom the VNTR pattern (of the child, the criminal evidence, or whatever else) belongs. Given, that probability might be 1 in 20 billion, which would indicate that the person can be reasonably matched with the DNA fingerprint; then again, that probability might only be 1 in 20, leaving a large amount of doubt regarding the specific identity of the VNTR pattern’s owner.

1. Generating a High Probability

The probability of a DNA fingerprint belonging to a specific person needs to be reasonably high–especially in criminal cases, where the association helps establish a suspect’s guilt or innocence. Using certain rare VNTRs or combinations of VNTRs to create the VNTR pattern increases the probability that the two DNA samples do indeed match (as opposed to look alike, but not actually come from the same person) or correlate (in the case of parents and children).

2. Problems with Determining Probability

A. Population Genetics

VNTRs, because they are results of genetic inheritance, are not distributed evenly across all of human population. A given VNTR cannot, therefore, have a stable probability of occurrence; it will vary depending on an individual’s genetic background. The difference in probabilities is particularly visible across racial lines. Some VNTRs that occur very frequently among Hispanics will occur very rarely among Caucasians or African-Americans. Currently, not enough is known about the VNTR frequency distributions among ethnic groups to determine accurate probabilities for individuals within those groups; the heterogeneous genetic composition of interracial individuals, who are growing in number, presents an entirely new set of questions. Further experimentation in this area, known as population genetics, has been surrounded with and hindered by controversy, because the idea of identifying people through genetic anomalies along racial lines comes alarmingly close to the eugenics and ethnic purification movements of the recent past, and, some argue, could provide a scientific basis for racial discrimination.

B. Technical Difficulties


Errors in the hybridization and probing process must also be figured into the probability, and often the idea of error is simply not acceptable. Most people will agree that an innocent person should not be sent to jail, a guilty person allowed to walk free, or a biological mother denied her legal right to custody of her children, simply because a lab technician did not conduct an experiment accurately. When the DNA sample available is minuscule, this is an important consideration, because there is not much room for error, especially if the analysis of the DNA sample involves amplification of the sample (creating a much larger sample of genetically identical DNA from what little material is available), because if the wrong DNA is amplified (i.e. a skin cell from the lab technician) the consequences can be profoundly detrimental. Until recently, the standards for determining DNA fingerprinting matches, and for laboratory security and accuracy which would minimize error, were neither stringent nor universally codified, causing a great deal of public outcry.



 
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Posted by on April 21, 2011 in Science

 

Memories of Midnight

It was the third day of my isolation from the world in the little cozy room of my hostel. I was trying to come over from the traumas which I have been getting in a regular interval of time for last few months. Like a very optimistic creature, I have been sitting in my room searching for all the happiness and hope left in my life. It was midnight and when the dim light, hustle of fan and noise from the ground floors became unbearable, I stood up, wore my jeans and left room with my cell phone switched off. It was dark outside. Night never comes in a boy’s hostel. But outside the cruel world sleep and wake up at fixed times. It was dark outside and I started walking towards the road which passed along our premises. The road generally remains empty during day also because it doesn’t lead to any important destination. But I have always taken that way in my life. I proceeded without looking back. I lost track for how much time I have been walking. I walked, walked and walked. At some places I heard my name being called by my friends and the people who care for me. But I didn’t stop. I put my head down so that I have not to look into eyes of anyone. Although I was alone. There was no one ever.

The only reason I have been walking was because I liked that particular path. I was committed to my self to take that only path. I walked for hours, for days, for weeks, months and then years. I stopped to take rest sometimes but never took a break. I never once got frightened. My hands, legs, body and heart got bruised with the thorns, ditches and insults of the path. But I never succumbed. There was a wish which I cherished, which I believed would come true when the road ended. And I continued walking.

After walking for years in the scorching sun and chilling colds, I ultimately reached there. It was stunning. It appeared to be a hilltop. I was filled with nostalgia, happiness, pain and joy all in once. When I approached closer, something happened which I never expected. It suddenly became very dark….dark as if it was midnight. I always feared nights. I never wanted to be awake in nights. I closed my eyes tightly. After some time I slowly opened my eyes. I hoped that it was dawn already. Yes it was. But not in the way I thought. The door in front of me was closed. On the other two sides there were walls. I looked behind in the hope that the way which brought me here was still there. But it was gone. There was only a very deep unending depth which meant end. There was no way back. I sat there on my knees looking at the door with tears in my eyes. Hoping that somebody would see it someday, I wrote on the door with the blood dripping- “Why she just can’t let me in??”

Disclaimer- A crap product of depressed state. Read with care. 😦

 
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Posted by on April 13, 2011 in Memories

 

32 facts about boys-

  • Guys don’t actually look after good looking girls, they prefer neat and presentable girls.

  • Guys hate flirts.
  • When a guy says he doesn’t understand you, it simply means you’re not thinking the way he is.
  • Guys may be flirting around all day but before they go to sleep, they always think about the girl they truly care about.
  • When a guy really likes you, he’ll disregard all your bad characteristics.
  • Guys go crazy over a girl’s smile.
  • Guys will do anything just to get the girl’s attention.
  • When you touch a guy’s heart, there is no turning back.
  • When a girl says ”no” a guy heart hears it as “try again tomorrow”.
  • You have to tell a guy what you really want before he gets the message clearly.
  • Guys love their  MOMS.
  • A guy would sacrifice his money for lunch, just to get you a couple of roses.
  • You can never understand him, unless you listen to him.

  • If a guy tell you he loves you once in a lifetime. He does.
  • Beware. Guys can make gossips scatter through half of the face of the earth faster than girls can.
  • Like eve, girls are guy’s weakness.
  • Guys are very open about themselves.
  • It’s good to test a guy first before you believe him. But don’t let him wait that long.
  • Guys hate it when their clothes get dirty. Even a small dot.
  • Guys really admire girls that like even if they’re not that much pretty.
  • If a guy tells you about his problems, he just needs someone to listen to him. You don’t need to give advice.
  • A usual act that proves that the guy likes you is when he teases you.
  • Guys keep secrets that girls tell them.
  • Guys think too much.
  • Guys’ fantasies are unlimited.
  • Girls’ height doesn’t really matter to a guy.
  • Guys tends to get serious with their relationship and become too possessive. So watch out girls.
  • Guys are more talkative than girls are, especially when topic is about girls.
  • You can truly say that a guy has good intentions, if you see him praying sometimes.
  • If a guy says you’re beautiful, that guy likes you.
  • Guys hate girls who overreact.
  • Guys love you more than you love them. If they are serious in your relationship.

 
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Posted by on April 7, 2011 in Love

 

Engineering Marvel- The Hoover Dam

It’s not the world’s biggest dam, but it was the one that changed the way we build them.The first of the large concrete arch dams that dominated the 20th century, Hoover also marked the birth of America’s dam-building boom. Its Depression-era construction cost $49 million and used so much concrete that engineers had to pipe cooled river water through the dam face to help the concrete cool faster.The sweeping, 60-story-high concrete arch, along with its water works, power station and intake towers, were all designed in classic art deco style, reminding us of the days when plans for public works projects included intricate stone and metalwork, ornate plaques, and elegant statues of massive seraphs guarding the gates.

Once known as Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the US states of Arizona and Nevada. It was constructed between 1931 and 1936 during the Great Depression, and was dedicated on September 30, 1935, by President Franklin Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives.

Since about 1900, the Black Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water and produce hydroelectric power. In 1928, Congress authorized the project. The winning bid to build the dam was submitted by a consortium called Six Companies, Inc., which began construction on the dam in early 1931. Such a large concrete structure had never been built before, and some of the techniques were unproven. The torrid summer weather and the lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned over the dam to the federal government on March 1, 1936, more than two years ahead of schedule.

Hoover Dam impounds Lake Mead, and is located near Boulder City, Nevada, a municipality originally constructed for workers on the construction project, about 25 mi (40 km) southeast of Las Vegas, Nevada. The dam’s generators provide power for public and private utilities in Nevada, Arizona, and California. Hoover Dam is a major tourist attraction; nearly a million people tour the dam each year.

Hoover Dam Construction

The Hoover Dam’s construction began in 1931, and it was completed five years later.   It was built as a source of hydroelectric power generation, to provide water for agricultural purposes and to prevent floods.

  • A conglomerate titled Six Companies Inc. was created especially to build the Hoover Dam.  The sextet of companies involved comprised of Morrison-Knudsen, the Utah Construction Company, the Pacific Bridge Company, the Bechtel Corporation/Henry J. Kaiser, MacDonald and Kahn and J.F. Shea.
  • When finished, the Hoover Dam stood as the largest electric-power generating site in the world, as well as the largest structure made out of concrete.
  • The Dam weighs over six-and-a-half million tons, and incorporates over three million cubic yards of concrete – enough to construct a motorway connecting New York to San Francisco!  Sited on the 18th longest US’ river, the Colorado, the Hoover Dam was named after then-US President, Herbert Hoover.  The body of water trapped behind the Hoover Dam, Lake Mead, took its name from the principal authoritative figure in charge of the Dam’s construction, Elwood Mead.
  • The Hoover Dam’s construction features 17 turbines, of which one is rated at 86,000 horsepower, one at 100,000 horsepower and the remaining 15 at 178,000 horsepower each.

Facts and Figures

  • Hoover Dam is named after Herbert Hoover, the 31st president of the United States. For some years, it was referred to as Boulder Dam
  • The backwater is named as ‘Lake Mead’ as ‘Elwood Mead’ was the principal authoritative figure in charge of the dam’s construction. Lake Mead is spread over 146,000 acres and it is recognized as the largest reservoir of the world.
  • Six Companies, a conglomeration of six well-known companies was awarded the contract to build the dam. The lowest wage paid to a dam worker was 50 cents an hour while the highest was $1.25!
  • During construction, 96 men lost their lives in various accidents. The mascot dog, the pet of all construction workers, was buried at the site of the Hoover dam.
  • Hoover dam was built near the border of Arizona and Nevada to control floods, to generate hydroelectric power and to provide water for agricultural purposes.
  • Hoover dam, being one of the seven modern engineering wonders, thousands of tourists visit Hoover Dam everyday. It is believed that rubbing the toes of the two 30 feet tall winged figures (made of bronze), standing on the Nevada side’s approach to the dam, brings good luck.
  • Here are some interesting Hoover dam construction facts. In all, about 16,000 employees were involved in the construction of Hoover Dam. About 3,500 people were employed at a time. About $49,000,000 were required to complete the construction of the Hoover dam.
  • The Hoover dam bypass project involving construction of a bridge whose arch span stretches 1,060 feet and whose deck stands 900 feet above the river, is also one of the wonderful projects of this century.

Hoover Dam Power Output

  • The Hoover Dam’s approximate annual power output is 4 billion Kilowatt-hours (KW-h), while the maximum power output produced by the 17 water turbines is a combined 2.08 Gigawatts.

Environmental Benefits

  • The Hoover Dam provides a vast supply of renewable energy, which is fed across a significant area of the US.  This type of energy has no associated greenhouse gas emissions, although emissions were created and released during its construction phase.
  • Once activated, the Hoover Dam allowed the Colorado River to be controlled, providing local farmers with a regular supply of water.

Environmental Drawbacks

  • The Hoover Dam had an immediate impact on local biodiversity.  While it created Lake Mead, it also stopped water flowing to the mouth of the Colorado River.  Four species of fish were killed to the extent that, in modern times, they have become regarded as endangered.
 
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Posted by on April 5, 2011 in Uncategorized

 
 
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