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Question about Northern Blot - (Dec/18/2013 )

I would be very grateful if someone provided me some hints to tackle this problem: 

A human gene with 4 exons and 3 introns has been identified.

Introns have 456, 1500, 224 and 524 pairs of nucleotides respectively.

Exons have 2300, 500 and 4600 pairs of nucleotides respectively. 

When performing a Northern Blot with a RNA probe for this gene in a human cellular extract,a pattern with 3 bands was observed in the autoradiography:

Each band corresponds to RNAm molecules of the following sizes: approximately 2700 pairs of nucleotides, 1200 pairs of nucleotides

and 1000 pairs of nucleotides. Explain the results of the Northern Blot.
Extra question: what would you do to improve the analysis?
Key Concepts: transcription, splicing, alternative splicing.
Thank you very much!! 




you have your introns and exons labelled in reverse.


mrna is produced from combinations of exons (alternative splicing).


the sizes of product are approximations (not exact).


Thank you! The number of nucleotides in the introns is irrelevant, isn't it? 


pretty much (at least, for your purpose)