Slashdot Mirror
Home DNA Sequencing
An anonymous reader writes "Wired is running an article about high-tech gifts for Christmas, including a home DNA sequencing kit targeted at kids for under $100. What's next, the Fisher Price Cloning kit?"
← Back to Stories (view on slashdot.org)
Why pay when you can do it for free?
Its not quite what it says on the story, its not DNA sequencing its just a DNA seperation kit using the bog standard ethanol prep which you can do with washing up liquid, salt and a bottle of (80%) Polish vodka. The electrophoresis step is quite nice using a battery to provide the DC current. However the kit is nothing you could not make yourself (Most of Molecular biology is really quite low tech the main requirement is getting pure reagents to do it with)
Thats not to say its not a cool gift/toy, at the very least the Centrifuge, and Electrophoresis chamber could probably be reused by the budding geekling
here is the link to the actual product.
Quite simply there is no sequencing ocurring. It's merely separation of DNA molecules. This will just tell you their size. There's not sufficient information in the article or the store blurb for me to figure out if restriction enzymes are being included, which would make things slightly more interesting. In the days before PCR and DNA sequencing was as easy as it is now, genetic tests were done via Restriction Fragment Length Polymorphisms, so your DNA would break up into differently sized bits depending on which sequence was present at a cutting site.
I took a little time to read the description of the kit on Discovery's website. It's much less than the /. post suggested. There's just some chemicals and a toy centrifuge to extract DNA. Actually there are ways to extract DNA with household chemicals, precipitate with isopropanol and spool on a glass or plastic rod.
So far it's only DNA extraction, cool as a science-for-fun thing, but nothing new.
The analysis part (with electrophoresis) seems to be fake (simulated, if you wish). The kit, according to the Discovery website contains
"DNA stain (fabricated to mimic real DNA)".
So, it's just a toy, cool, but nothing that'll allow Junior to test his paternity or do any real DNA analysis. There are educational kits that provide real DNA analysis in a classroom environment (like the Biotechnology Explorer program from BioRad), but they still require teacher's supervision.
Another poster gave a good explanation of the applications of sequencing. I'll give you a quick explanation of how it is done:
...
1. Obtain a pure sample of DNA to sequence. You have to know a little bit of the sequence at the start (not a problem - when you sequence an unknown DNA sample you usually chop it up into bite-sized chunks and insert them into bits of bacterial DNA to make lots of copies of them - this means the unknown DNA has bacterial DNA on either end of it and you already know the sequence of that part).
2. Make a short strand of DNA that binds to the known portion of DNA sequence at the start of unknown portion. These are called primers.
3. Mix the DNA to be sequenced with the primers, heat them up and cool them. This results in long pieces of uknown DNA with the primers stuck to the beginning.
4. Throw in the building blocks of DNA - but a small portion of them are essentially defective and marked with fluorescent tags.
5. Throw in DNA replicating enzymes - these guys look for primers and try to copy the unknown DNA starting at the side of the DNA with the primers attached.
The DNA replicating enzymes will copy the DNA until they accidentally grab a building-block which is defective (which happens a small portion of the time - since most of the building blocks in the mixture work fine). At that point the defective building block is attached to the end of the DNA strand and that strand cannot be copied further.
At the end you end up with a mix of DNA strands that look like:
1. Only one step of the DNA ladder copied - because the first block grabbed was defective.
2. Only two steps copied - the second block was defective.
3. Three blocks copied.
N. The whole strand is copied.
Each of these DNA strands is one step longer than the strand before it. Each has a fluorescent tag at the end - since each ends with a defective block.
You then put this mix of partial strands onto a gel and apply an electrical current - the bigger strands move through the gel more slowly (they get stuck in the pores in the gel).
You end up with a gel with a long ladder-like series of bands - each band is a DNA strand one step longer than the band before it. Each is fluorescently tagged.
Now here is the magic - back when you put the defective building blocks in you actually used a mixture of four blocks (the four types of steps in DNA) each with a different color tag on it. So each band is a different color - corresponding to the color of the last step that was added to the chain. The pattern of colors corresponds to the sequence of the DNA.
I tried to simplify this explanation for those with only a basic understanding of biochemistry. There are various ways of doing DNA sequencing, and these days much of it is automated.
Oh - where the computers come in is this:
A gel like the one I described can only handle pieces of DNA up to about 400 steps long. That means that you can only sequence 400 bases at a time (a base is a step in the DNA ladder). A human being has 4 billion bases in their DNA.
The way you sequence the whole human genome is to chop it up into lots of 400 base units. You actually take lots of copies of the human genome and chop it into lots of random pieces. Then you sequence pieces until you're sequenced about 40 billion bases. Then you have a computer run through the sequences looking for overlaps. The computer will find lots of regions that are sequenced several times, and some regions that weren't sequenced at all. However, it will give you a pretty good sequence of the overall genome, and then some careful followup work can fill in the gaps (the followup work is less easily automated, so they try to get most of it using the random method).