Difference between EST and full length c-DNA?

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chandan_10_08
chandan_10_08's picture
Difference between EST and full length c-DNA?

Hello Everybody,
I'm new to field of Genomics. Can some one explain the difference between an Expressed Sequence Tag and full length c-DNA?
I'd also like to does full length c-DNA derived from mature mRNA or whole mRNA( before splicing)?
 
 

ryan_m
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chandan_10_08 wrote:

chandan_10_08 wrote:

Hello Everybody,
I'm new to field of Genomics. Can some one explain the difference between an Expressed Sequence Tag and full length c-DNA?
I'd also like to does full length c-DNA derived from mature mRNA or whole mRNA( before splicing)?
 
 

 
Hi there.  An EST is a single sequence read produced from one of the two ends of a cDNA (primer can be either the vector or a polyT, which primes in the polyA tail).  The only difference between this and a full-length cDNA is that in the latter, the entire cDNA insert is sequenced (usually by primer walking, but at the very least, using 2 opposite end reads).  cDNAs are always generated from mature mRNA, which is spliced.

Ivan Delgado
Ivan Delgado's picture
Hi Chandan,

Hi Chandan,
Ryan's explanation is right on. I only want to add that the technology of EST generation (sequencing large numbers of cDNA ends) was developed years ago to get a broad idea of which genes are being expressed in a given experiment/sample. Its intent is basically to get a crude yet broad measure of which genes are being expressed and at what level (the more ESTs you get for a particular gene, the more highly expressed the gene is).
A cDNA on the other hand is the complete sequence of the given gene being studied. One thing to keep in mind when comparing ESTs and cDNAs is that some genes are alternatively spliced. For example if you have a gene with four alternatively spliced mRNAs, all with the same last exon, then your EST and cDNA information could be very different: when you study the cDNAs you would find four; but when you look at ESTs (for simplicity only 3' end sequences) you will not be able to distinguish the different splicing variants and assume that all the ESTs came from one cDNA.

chandan_10_08
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thank u Ryan, and Ivan for

thank u Ryan, and Ivan for the information