# Thread: The Size of an allele?

1. Hi All,

I am doing a presentation on Alzheimer's Disease, and want to emphasise to my audience how minutely small an allele is within the human body. I was wondering if anyone knew the rough length/ size of an allele on a chromosome in the body, and if so what it would be proportionally compared to? (e.g. 1/1000 of the size of a grain of rice or anything along those lines) I know this sounds slightly ridiculous, but I think it will really help prove my point in my presentation.

Any help appreciated,
Thanks

2.

3. Since an allele can be one gene or a grouping of genes you might be better to indicate the size of a normal strand of DNA and how many gene sites they normally carry.
A gene is really just a small piece of the string of the acid base pairs that make up the DNA molecule. It does not have a specified length.
A DNA strand can carry thousands of genes though, and you need a strong microscope to see them. Maybe that information with a picture of cell mitosis would get the idea across.

I think comparing DNA to the size of a rice grain would be tooo far out of scale to be meaningfull, but comparing a human body cell to the diameter of a hair might be workable.
If people understand how small a single cell is you can show them how much smaller a DNA molecule is, and then how much smaller genes are.

4. I doubt the relative size of a gene is really all that important to whatever point you are making.

Anyway, since a typical human gene averages (let's ignore the massive variation) about 12 kb, this means that the average gene has a length of approximately 4 micrometers, if it were to be laid out. In the cell it'll be folded in all sorts of ways so that this number is probably rather meaningless.

5. Well.. If you stretch the DNA from a single cell (excluding the mitochondial DNA), is about 2 - 3 meters. 100 trillion cells in the human body. Put all the DNA you got on a line, and you will reach 300 trillion meters. 300 billion kilometers. And with the distance from the earth to the sun is about 150 million kilometers so you could stretch your DNA from the earth to the sun 2000 times.

Could be cool to know