Question

You have been given a 1.0 kbp human genome fragment that does not contain any repeated sequences. Your plan is to use it as a probe for a Southern Blot containing your friend's genomic DNA. You prepare your gel by digesting with the following restriction enzymes in the following lanes:

Lane 1: size marker

Lane 2: EcoRI Lane

3: HindIII Lane

4: BamHI

Your friend happens to be homozygous for the region you are probing. Does that mean you will only see one band in each lane? Explain. 10pts

Answer 1

When we are using the restriction enzymes , they will cut the genome at many places, based on the number of restriction sites present. If EcoR1 has 3 restriction sites, there will be 4 fragments and based on the size of the fragments, they form different bands. Similarly other restriction enzymes also cut the genome based on the number of restriction sites present for each restriction ezyme. The number of bands formed depends on the size of the fragment length. Smaller fragments move faster through the gel and larger fragments move slowly through the gel. Once the process is complete, DNA binding stain can be used to clealry visualize the bands formed and also the size of the fragment by comparing it with the standard lane. That is how we get different bands in the gel.

When the alleles are similar, their fragment length will also be same. So they form a single band together. But there will be other bands forming also based on their restriction sites and fragment length.

So, you will see more bands on the gel. But probe may recognize only one that is made to identify the alleles in the genome.