Monday, January 23, 2012

Born Identity: DNA Testing


The world is full of obvious things which nobody by any chance ever observes.
– Sherlock Holmes

It was said a century ago when there was no concept of DNA. But today DNA identification is used as the ultimate and irrefutable tool in criminal justice system and paternity disputes, immigration, endangered species movement, among many other applications. Forensic science has moved a long way from the time of Sherlock Holmes and the obvious things are surely observed in specialized laboratories with utmost care.

On surface, it seems that the technology should be ideal for routine use. But there are problems which hinder its wide-scale use in daily life. In the CSI: Crime Scene Investigation or SVU: Law and Order series of the cable TV, investigators are shown to be able to solve any mystery within few hours with the help of DNA analysis. But in reality it is far from the truth. With so many complexities involved, it takes a good amount of man hours to generate a reliable DNA profile. 

DNA or Deoxyribo Nucleic Acid is a nucleic acid present in every cell of any organism, including humans. It is called the User Manual or a Master Code of the body. Everything we do from birth to death is controlled by the information encoded in it. It is composed of small units called nucleotides and denoted by 4 alphabets, A, C, G and T. However, a large amount of this DNA is currently considered as junk DNA and it is usually in the form of repeats e.g. AGTA. These repetitions are of interest to forensic scientists. Humans have different number of repeats at different places on their DNA. These are in the form of successive repeats and are thus called Short Tandem Repeats (STR). For example, one person may have 6 repeats of AGTA while another may have 7 and some other 8 and so on. These are called alleles and determining how many repeats a particular location or locus (plural loci) has is called allele count. For example, the 6 repeat is called allele 6 and so on. The more loci we use for allele determination, the lesser chance we will have of a random match. CODIS (Combined DNA Index System, USA) is a database of DNA profiles which uses 13 loci of the DNA to identify different humans. The data from all these 13 loci are called a DNA Profiles. CODIS is a database which stores DNA profiles from convicted offenders as well as evidence recovered from a crime scene and used for identifying a match. By using this system, there is a probability of 1 in a few trillions that a DNA profile from one human will exactly match the profile from another individual except identical twins.

The first step of DNA testing is PCR or Polymerase chain reaction which amplifies the sample DNA into amount millions of copies which can be used for testing. We only need to amplify the regions of interest and not the whole DNA. This is accomplished by providing the starting points of amplification in the form of short DNA pieces or fragments, called primers. It could be compared with the postal service. If we write the proper address, we can deliver our mail to only one specific address in the whole world. These primers are labeled with dyes so that the amplified DNA can be visualized for allele count. The next step is generation of DNA profile with the help of electrophoresis in which depending on the size, DNA fragments move differently. For example a 100 base pair fragment will move faster than a 150 base pair fragment. A standard or ladder DNA is also run along the sample so that size is determined using this is a reference. All alleles of the sample DNA are determined and this information is stored in the database for future use. If another profile having exactly the same DNA profile comes, we can say that it is the same person or a twin of that person. 


Simplified DNA Profiles of a DNA sample found at a crime scene and two suspects. You can find which one is the true perpetrator


Each person inherits one allele from father and one from mother. So if we have DNA samples from a parent and a child, we can determine the other parent. For example, if a child has alleles 5 and 6 and mother has alleles 6 and 7 then we can be sure that allele 6 in the child is contributed by the mother and hence, allele 5 must be contributed by the father. This is done for all the 13 locations and then a match or mismatch is confirmed. This technique is used in resolving paternity disputes.

A modern DNA Profile as you would see on TV, like in CSI.

The most important point in DNA testing is collection of evidence and its interpretation. Hence, in many cases, convicted people are exonerated after many years, on the basis of DNA testing. As in CSI, Gil Grissom says: “You can be wrong, I can be wrong but the evidence is just the evidence.”





P.S. This is an old post but I posted it again for 2 reasons:
1. In the stories about Sherlock Holmes, there was a bit about DNA Testing and some people were asking about it.
2. I would be writing something on DNA in the coming posts and that is why I wanted to make kind of a foundation.


57 comments:

  1. nice and very informative..thanks for sharing...

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    1. thank you very much hope it is helpful :)

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  2. excellent work israr ... u have given a very crystal clear image of silicon chip integrated by nature inside a living cell.i hope in future you will write more about the uses of PCR techniques.

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    1. thank you almas... i am glad you liked it.. yes i will try to contribute humbly :)

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  3. @Israr: Plz give a more detail of using DNA for forensic cases.

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    1. Thank you for the suggestion... i will try to write in more detail in the future :)

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  4. Great Israr, ur feature is very informative 4 such peope who do not know much about that like me, I hope you will write more about such senstive topics. Your way of explaintion is very good, one can easily undestand what you write. Keep on trying may Allah help you.

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    1. thanks kiran for reading and liking... i am glad you got some info from this about dna testing.. i just try my best..and i am happy that you people get something out of my writings :) keep coming back... :)

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  5. Thanks for your share! I think this information is helpful for everyone. I'm doing practice GRE in masteryourgre.com . I hope it's useful for GRE test takers.

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  6. Genetics has always fascinated me! It's amazing how quickly DNA can be processed and analyzed when they only have one hour minus commercial breaks in which to solve the mystery.

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    1. lolz...but its very complicated thing and the tv people only shows the results and not how this whole process is carried out or else it would be too boring for the viewers :)

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  7. Though there are ethical issues regarding the use of DNA in some instances ("cloning"), I have no scruples about them. I think it will eventually be an important part in the preservation of species, including ours for threats of extinction.

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    1. there are issue with every new technology but we have to weigh the pros and cons of any new technology and accordingly use it...

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  8. Wow Science. This really helps! This post has a lot of informations! Keep it up! =)

    Thanks =)

    http://fayerydust.blogspot.com/

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    1. thank you for reading and liking it..i am glad you got something out of it :) keep visiting... :)

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  9. Yep it takes hell of time to generate a criminal profile and to interpret possible out come even having technology available :)

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    1. yes niaz i understand your situation... :) in your case it take more than that to generate a profile :P

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  10. Atif Khattak - Buddy of CEMB16 June 2011 at 16:42

    As I am a professional of Accountancy, obviously not a biological scientist / professional, but today I felt myself as a DNA proficient after reading miraculous wordings narrated by an intellectual Phd scholar Israr buddy. Reason behind my proficiency is “expression” which is so awesome that even a baby can understand. DNA testing is one of the emerging instruments used frequently to cater dubious paternal cases of the modern arena of this world.
    Wonderful effort once again, admired the element of “Quality” in it.

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    1. Buddy... i am very pleased that you could understand this thing..i tried to write if for people who are not biologists and they want to know something about dna testing... keep visiting and reading :)

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  11. Simply the best,,,,,,,a facile blog with retaining agility,,,,,as far I know Misterio is a thesaurus, but in his writings he really avoid to use troublesome words..... thats show his intentions to prevail knowledge... I am proud of u man

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    1. thanks dear... i am glad you read and liked it... it is due to the esteemed company of friends like you that i am able to write whatever i can :) keep reading :)

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  12. Fascinating stuff Israr - I await your future posts on DNA with great interest,

    Anna :o]

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    1. thank you for liking it... i do hope to post something in the next month on DNA :)

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  13. Israr i like the added pics it remind me the genetics i studied in my graduation. and i found the criminal suspected 2. ;P

    thats what the only thing when i read my nerves get relaxed as i love science being a science person.

    keep writing waiting for the next article based on DNA :)

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    1. wow... you are a genius... so now even you can solve the mysteries of DNA testing :P

      you are the first person in the world who gets relaxed by reading science :P

      thank you for liking...hope to post something on DNA next month :)

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  14. Fascinating read! :) You explained in great detail but it was really crisp at the same time. Was enlightened! :) Forensics and Sherlock Holmes always enthrall me.

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    1. Thank you for liking it... i am glad you like S.Holmes and Forensics and coincidentally i have posted all these this month :)

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  15. Collection of evidence and its interpretation is really challenging. It’s so time consuming for the investigators to generate a reliable (Deoxyribo Nucleic Acid ) DNA profile. Good scientific development indeed.
    DNA matching for punishing criminals and in paternity testing is amazing.
    Is there a psychological DNA for controlling the "out of control" ruling elite and the chamchas?

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    1. hahaha...no i think there is no such test..and i am glad otherwise these elites would have patented it and we the commoners would never be able to access it :)

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  16. Pretty complicated actually! :) Any evidence can be used against the very person who is supposed to be saved by Law. Since this DNA is so complicated to understand, it can be misused. But then, as you say, there are advantages and disadvantages to any scientific method and I just hope that all the analysis happens in an unbiased manner. There are always people who would want to influence as there are people who want to get influenced!

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    1. yes of course... the chain of custody is the foremost important thing and even a slight doubt on its integrity nullify the rest of the process...so of course even the process is near fool-proof but the executors are humans and there are good and bad humans...so...

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  17. Israr@
    u realy made it easy by ur discission for a person like me who do not have sufficent knowledge about DNA testing proces..... u must write more about that i l enjoy all that..... keep it up. u posted it again, no problm bcz i had forgotten about that-p

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    1. i am glad that you liked it...and yes i understand it is very difficult for people outside the subject but i am glad you people get at least something from this post... a general idea is all that i meant you people to get... :)

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  18. Excellent explanation of the process. Many thanks for.

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    1. Thank you for reading and liking... somehow i feel like someday you are going to write a poem about this too :)

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  19. That was so much information and technical too! :P Tried my best to understand it, very well written.

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    1. I am glad you liked it...yes i feel like it was a bit technical but could not help it... the TV stuff is so superficial and unrealistic so i was thinking to write something realistic and yet simple to understand...

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  20. Informative post. I love the quote from Sherlock Holmes :)

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    1. thanks for reading and liking it..i am glad you liked the quote :)

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  21. My friend Israr. Happy Saturday! (or Sunday depending which time zone you're in)
    I refuse to watch CSI or Law & Order...these are just too unrealistic. I much prefer First 48, Crime 360 & Investigation Discovery. These deal with DNA & real life scenarios all the time.

    You're very good & obviously know your stuff. This write-up of yours was very informative. If I had you as my partner in Science, I'm sure I would have sailed through (smile).
    Thanks for sharing.

    Today (Saturday) is my 1st Blogoversary & I've prepared a special post for my friends & readers. You've been instrumental in supporting my blog & as a token of my appreciation & gratitude for your loyalty, I've made a special gift for you. I hope you will honor me by accepting it. The gift is at the end of the post. Click on it to open in a new window so you can copy/download to your blog
    Enjoy the rest of the weekend & I look forward to seeing you soon!

    Special Celebration (Part.2):It's My Blogoversary!

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    1. Happy Monday :) yes CSI is so superficial and SVU also...but they have to cater to the general veiwers who are not necessarily interested in the technicalities.... I am glad you found it informative ...hahaha...then we would be having scientific poetry? :P

      I visited your blog... many many best wishes :)

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    2. Hello Israr.
      LOL...scientific poetry...now that would be a first...and we would be the best in class no?

      From the day I met you, you've always been a loyal supporter of my blog & I thought it only fair that you be recognized for that. There are no losers in my blog...everyone is a winner (smile). I hope our friendship will continue for many more years to come.
      You make me very happy for accepting the Award. Thank you.

      have a great week ahead, my friend!

      BTW, your replies to Princesa Fiona & Balqis were funny. I hope they see it & respond!

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    3. off course what else can we make? scientific poetry is the thing :) surely i would gladly accept any award :P
      and i hope they both read my replies and respond...have a great week :)

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  22. It broadens my knowledge reading this informative post. My arts' mind is trying to digest the scientific terms here. I'm glad you have this re-posted. At least, I'm ready for your up coming post. :)

    Sorry to have missed this and other posts. There seemed to be a lapse of time but rest assured I'll be around. :)

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    1. well... i wonder you would start writing haikus about DNA :P
      this is criminal negligence on your part...how could you be absent? :@

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    2. Please, pardon me, Dr!

      The idea of writing Haikus about DNA is great. :p

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    3. ok this time you are pardoned...

      ahan... so you should pay me the royalty of these haikus because i gave you the idea :P

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  23. very informative post bro!

    though i am not concerned with this field but i learnt much about DNA from this post

    thanks for sharing such information with us
    and sorry for reading this post so late

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    1. thanks bro..
      yes you are an engineer but see the DNA testing is always in the news so you should have a basic idea of it :) i am glad you learn a few things :)

      yes i observed you are late..maybe busy with exams :) BEST OF LUCK...

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    2. thank you

      yes i was busy with exams.

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  24. Replies
    1. Welcome to our blog...

      thanks for reading and liking :)

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  25. There are now several DNA databases in existence around the world. Some are private, but most of the largest databases are government controlled. The United States maintains the largest DNA database, with the Combined DNA Index System, holding over 5 million records as of 2007. The United Kingdom maintains the National DNA Database which is of similar size, despite the UK's smaller population.Court DNA Testing

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