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Northern blotting is a procedure used to detect mRNAs that match to a specific DNA sequence. The isolated RNA is run on an agarose gel which separates the RNA by size. The RNA is then transferred to a membrane which is then treated with a small DNA probe. The DNA probe will hybridize (form base pairs with a complementary sequence) with the RNA in the membrane. The probe contains a dye that allows it to be visualized.

Due to the specific nature of the probe's base pairing, only mRNA that has a specific sequence complementary to the DNA probe will be visible. In this way, the size of mRNA from a specific gene can be determined.

Upon performing a Northern blot using mRNA isolated from the fruit fly (Drosophila melanogaster), you find a possibly surprising result. You find five distinct bands of different sizes in the blot. You are able to confirm that the DNA probe you are using is specific to only one locus in the genome and that none of the bands are artifacts (therefore all of them are RNA which match the DNA probe).

Which of the following is the MOST likely explanation for this result?

A

The gene in question is alternatively spliced, leading to different length mRNAs from the same gene.

B

The gene in question occurs multiple times throughout the genome, with slight differences.

C

Different levels of the gene's expression in different tissues lead to the different band sizes.

D

The different sizes are due to the 5'cap and poly-A tail being added to the mRNA.

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