MadSci Network: Genetics |
Hi, Good question! In the case of bacteria like E. coli, most people would say that on average, one gene (which makes one protein) is about 1000 base pairs long. It is also pretty well accepted that bacteria don't have a lot of 'junk' DNA - the DNA found between genes for which no function is known (note that this is probably not 'junk', it's likely to be important for things we don't know about yet!). Given the average gene size, and the fact that almost all of a bacterial genome consists of genes, one can easily estimate the total number of proteins that could be made. So in this sense, one could say there is a kind of rule dictating how many proteins should be made from a genome of a given size. There are other things going on in eukaryotes that make the picture complicated. They have introns in their genes, meaning that the length of a given gene is not necessarily reflective of the size of the protein it can make. In addition, the eukaryotes have a lot of DNA between genes, which doesn't code for proteins. We don't really know what most of this does (this is the so-called 'junk' DNA - but I repeat, it's probably not junk!). In fact, in humans there is less DNA in genes than there is between genes. So the rule doesn't hold true in these creatures. There is more than this, I suggest getting into the library and looking at some of the newer genetics and genomics text books.
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