Question

The BRCA1 gene is very large, spanning roughly 100,000 base pairs. However, the functional mRNA from this gene is only 7,800 bases long. This difference is best explained by:

	A.	Only a small region of the gene called ‘the exons’ are transcribed.
	B.	The primary transcript is processed to remove many large introns.
	C.	Unneeded regions of the mRNA at the 5’- and 3’-ends are removed during processing
	D.	The mRNA is partially degraded after it is transcribed.

Answer 1

The difference is best explained by the fact that the primary transcript undergoes post transcriptional modification during which the intron region is spliced off and the exons are joined. However during transcription whole gene is transcribed including both exons and introns. So the correct answer for this question is (b).