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Asked by sereneisnotonfire to Judith on 15 Jun 2012.
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Judith Sleeman answered on 15 Jun 2012:
Several ways.
Using the sequence of the DNA you’re interested in, you can search a data base of the whole genome of the species the DNA is from. The results will tell you whether it’s a gene or not.
You could use a Southern Blot. To do this, you take genomic DNA, cut it up into shorter lengths of DNA using restriction enzymes from bacteria. Then you run the DNA through a gel using an electric current: DNA has a negative charge so will run towards the anode, smaller bits of DNA will run faster than larger ones. Then you transfer (or blot) the DNA from the gel onto a thin membrane. Next, you label up the DNA sequence you are interested in to use it as a probe (always used to be with radioactivity, but there are safer ways now). You add the probe to the blot overnight in a hot oven so that it sticks to the DNA on the blot if it has the right sequence. Next day, you wash off the probe that hasn’t stuck. If you put a sheet of photographic film on the blot, the film will turn black but only where the probe has stuck to the DNA. If the DNA sequence of the probe is a single copy gene, you will get one black band on the gel. If it’s a repetitive sequence, then lots of the bits of DNA in the gel will have the probe stuck to them, so you’ll get lots of bands or a big smear.
In an intact nucleus, or on chromosomes taken from a nucleus, you can use fluorescent probes (like the FISH ones Chris uses) to show where your DNA sequence is. If it’s a single gene, you’ll get two cute little dots. If its a repetitive sequence, you’d get much more widespread staining. I found this on google:
They’re not a company I’ve heard of, but the pictures are great!
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