I was discussiong DNA with a friend of mine and we came to a point of contention regarding DNA sequences. I feel quite certain I read once that you can swap the order of sequences with little effect but my friend was convince that the result would give, essentially goo.

To illustrate the argument lets say I have a DNA sequence
.... A G C G T T T A G C T C G C A A A T C G ....
and I took on section and swapped it with another
... A G C __ G T T T A  __ G C T __ C G C A A  __A T C G ....
... A G C C G C A A G C T G T T T A A T C G ....

This isn't the best illustration because the way I remember it is large chunks were swapped, say if chromosomes were swapped.

Anyway, the question. How important is order to DNA? Can you swap genes in sequence and get the same result? ie. say baldness gene is base pairs 20-35 what if i changed it to 69-84?

I'm assuming this isn't homework as I can't imagine a biology teacher using the example you cite. So firstly, the gene for baldness (APCDD1) is certainly not a mere 15 bp, it is some 100x longer.

Genes are generally in the order of hundreds to thousands of base-pairs. I think you are getting confused between swapping DNA sequences (a kin to your example) and define coding regions / genes.

In your example, you have just effectively mutated a short sequence of DNA, which isn't the same as swapping the order of genes; your example would likely be deleterious to whatever gene you did this within.

With regards to what I think you're asking, in some circumstances you can change the position of whole genes within the genome (and this depends heavily on what the gene is, what the organism is, how those genes are regulated, whether they are genetically linked with other genes etc). Suffice to say, you can do it in bacteria, so long as you also move the control element for the gene as well, and consider the above caveats); thus at one level you could say the DNA sequences had been swapped.

There are natural process of recombination that occur during sexual reproduction in higher organisms, however even here it the alleles (the variations of any give gene) that are swapped between parental DNA, but crucially they still occupy the same locus (position) on the DNA, thus the actual order of genes themselves doesn't change. Chromosomal rearrangements can and do happen within populations, however it id difficult to predict the outcome of such phenomena, or indeed whether they will be viable.

Last edited by Jim Caryl (23rd Jul 2010 15:57:14)

Hi Nick -
I just want to flesh out Jim Caryl's answer a little.  Genes are complicated structures.  A typical gene consists of not only of the protein coding sequence, usually broken up into exons, but also cis regulatory sequences consisting of clusters of protein binding sites that define when and where the gene is expressed. Cis regulatory sequences are usually close to the promoter of the gene they regulate, but sometimes they can be hundreds of kilobases, if not gigabases away.  Interspersed between the protein-coding exons, the cis-reg sequences and so forth are often stretches of DNA that are clearly non-functional.  For example, you can find dead viruses, transposable elements, or highly repetitive elements like GGCCT a thousand times in a row.  On top of that, genes exist in a particular chromatin (DNA plus all the proteins it binds to) environment in the genome.  Some areas have "open"chromatin and the genes are highly expressed, in others the DNA is locked down and basically inaccessible to polymerase.  So, you can swap, delete and rearrange sequences within a gene, as long as you don't harm the functional elements of the gene.  Sometimes the functional elements are easy to predict, such as the protein coding sequences.   Sometimes these are hard to predict, such as cis regulatory elements, which lack the regularity of the triplet code for proteins.  And sometimes these are downright impossible to predict  - for example, if I delete a large intron am I now changing the time it takes to make the mRNA in some crucial way that affects some regulatory pathway the gene is involved in?  You can also swap the order of genes, and this does happen naturally, as long as you don't separate the rest of a gene from a critical cis-regulatory element, or otherwise greatly change its expression.