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How DNA Profiling (or DNA Fingerprinting) Works

Let's Review:

The band in lane 1 in the gel shown at left (scroll down to see below) corresponds to the following sequence:

-AAGTGATAGATAGATAGATAGATAGATAGATAGATAGAATC-

It is 41 bases (or nucleotides) long. In this example, the flanking sequences consist of 9 bases (although in reality flanking regions are typically much longer). The eight four-base repeat units (GATA) make up the remaining 32 bases. How long would you expect an allele from this same locus to be if it had 10 repeat units?

Try again. Make sure you add up the number of bases in the repeat units and the flanking sequences.

Correct. For this sequence, an allele with 10 repeat units would be 49 bp long.

The fragment corresponding to the 10-repeat allele from this same locus would migrate down the gel at a rate that:

Try again. Remember that larger fragments migrate slower than smaller fragments.

Correct. An allele that has 10 repeats would migrate slower than the current band with eight repeats.

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