Biology Practice Problems PCR and Dideoxy Sequencing Practice Problems Solution: A DNA fragment was sequenced using dideoxy DNA seq...

Solution: A DNA fragment was sequenced using dideoxy DNA sequencing. In this procedure, ddATP was tagged with a green dye, ddCTP was tagged with a blue dye, ddGTP was tagged with a yellow dye and ddTTP was tagged with a red dye. The primer used had the sequence 5'-GACTC-3' . Given the gel electrophoresis representation shown below, what was the sequence of the DNA fragment (template strand)?

Problem

A DNA fragment was sequenced using dideoxy DNA sequencing. In this procedure, ddATP was tagged with a green dye, ddCTP was tagged with a blue dye, ddGTP was tagged with a yellow dye and ddTTP was tagged with a red dye. The primer used had the sequence 5'-GACTC-3' . Given the gel electrophoresis representation shown below, what was the sequence of the DNA fragment (template strand)?

Solution

Based on the dye tags, we can determine that the corresponding bases in each band is as follows:

Since electrophoretic profiles usually put the well above in these kinds of data, it can be assumed that the band that traveled farthest is the base below, which is A. Since this is the smallest fragment for this sequence, it is the starting base for the newly-synthesized strand. 

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