task An autoradiogram of a sequencing gel in a Sanger sequencing procedure is sh

Question

task

An autoradiogram of a sequencing gel in a Sanger sequencing procedure is shown below,
containing four lanes with DNA fragments with each lane representing the added ddNTP
together with a mixture of dNTPs (“lane G”:ddGTP added to reaction, “lane A”:ddATP added
to reaction, “lane T”: ddTTP added to reaction and “lane C”: ddCTP added to reaction).
a) Determine the sequence of the DNA fragment

b) Suppose that a Sanger sequencing procedure shows that the template strand sequence
is 5´-TGCAATGGC-3´. Sketch the gel pattern on an autoradiogram that would lead to
this conclusion.

Explanation / Answer

A dark band in a lane indicates a DNA fragment that is the result of chain termination after incorporation of a dideoxynucleotide (ddATP, ddGTP, ddCTP, or ddTTP). The relative positions of the different bands among the four lanes, from bottom to top, are then used to read the DNA sequence. The sequence of DNA fragment is;

5'-ATGTTCTTTTCTCCTGCCCTTT-3'

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