Why there is only one band on agarose gel, while there are 23pairs of chromosomes in diploid human cell?

Question

there are 23 pairs of chromosomes in diploid cell of a huamn , all chromosomes vary in length and base composition, so there should be 23 bands, but wen DNA extracted form cell is run on agarose gel, there appears only one band.

Answer 1

There SHOULD be different bands, if you did everything correctly. The purpose of running them on a gel is to separate them by size: since DNA has a constant size:charge ratio, the applied electric force makes smaller sequences run further.
Did you get a clear band or a smear? If you ran a ladder, what was the approximate bp length? It could have been a conglomerate. How long did you run it? Maybe the cs didn't have time to separate. The extraction might also have cut up the DNA, unless you followed the protocol exactly. Or, your gel is not of the correct concentration in order to accurately separate molecules of this size (they're pretty freakin big).
Good luck figuring it out!

Answer 2

I suspect that they are simply too large to separate on a standard agarose gel. Human chromosomes are massive molecules, ranging from about 50 to 250 million base pairs each. That, along with the proteins that go into keeping the DNA all nicely bound up, makes for a very large molecule that won't migrate far on any gel without exceedingly long runtimes or specialist techniques. Straightforward agarose gel electrophoresis is unlikely to separate them. If the gel is dense enough to make the distances between them significant, the run time will be huge. If it is loose enough to allow the DNA to migrate into the gel any significant distance it is unlikely to have the resolution required.

Additionaly, if you just do a crude DNA extraction you will end up with a tangled mess of DNA that won't readily separate. Only during cell division do the chromosomes become the neatly packaged discrete units we are familiar with. During most of the cell's life the DNA is only loosely wound, and you certainly cant visually separate the chromosomes. Just to complicate matters further, when they do condense they are long, thin molecules, and these usually migrate differently. Gell electrophoresis is based on the idea that the molecules being separated are roughly spherical, or at least that their orientation doesn't matter. Chromosomes are very long molecules, and that tends to affect their migration too.

Answer 3

Why should there be 23 bands when all of them are nothing but DNA ?? Even though there are 23 pairs of chromosomes the basic elements are ade, gua, cyto and thy rite