Thursday, May 1, 2008
How do new genes arise?
Serious Cat: "Get busy, or you are fired!"
I have a very bad habit. Once I go on a school holiday, I end up thinking about studies. Proof that you don't miss some things until it's gone. And since anyway I'm also writing up the seminar/workshop proposal for Tridansh, I get to kill 2 birds with 1 stone (hmmm, violent imagery for a common phrase, time to change it?)
I was lying in the bitter cesspool which is known as my bed, trying to get more sleep than I ever need, when something popped in my head (No, it's not a blood vessel, Ben and Spen, you can be sure I won't be in a body bag that soon). How did new genes come about? We all know that higher organisms have more genes and larger genome sizes than the lower ones, until it reach a certain point (C-value paradox, imagine the maize plant having a bigger genome than us).
I got out the Albert's Molecular Biology of the Cell 4th ed to look for the answers. Quite fascinating. It seems that new genes can only arise from existing genes, which explains the gene families and superfamilies. 4 ways how gene innovation is performed: Intragenic mutation, Gene duplication, DNA segment shuffling and horizontal transfer. I would love to put up the diagrams on the 4 known ways of gene innovation, but i'm afraid of copyright infringements, which would mean the demise of my blog.
1)Intragenic mutations refers to the internal mutation within the DNA sequence of the existing gene.
2)Gene duplication meant exactly what it says: another copy is made. This also explains redundant genes, which can sometimes play a vital role if the original is mutated. This method gives rise to gene families and superfamilies. An example would be Bacillus subtilis, 47% of its genes have 1 or more relatives. There are 3 terms used to describe relationships: Orthologs, paralogs and homologs. orthologs refers to 2 genes that are derive from 1 common ancestor gene of the last common ancestor of the 2 species. Paralogs means that the related genes are result of a gene duplication event within the same genome. Homologs simply are either orthologs or paralogs, it's a general term for both.
3)Segment shuffling means that 2 genes "cross over" one another, creating 2 different gene. I don't really know whether this is translocation and that whether the rejoining of the segments is based on homologous recombination or not. If anyone knows, please tell me.
4) Horizontal transfer is the mixing of genes between 2 organisms, even different species. Think conjugation in bacteria, gene reassortment in intermediate hosts for viruses. Sex is also a type of horizontal transfer within the same species. Vertical transfer just means transfer of gene from parent to progeny, during mitosis.
I leave you with 2 questions. Within a genome, how would one know which gene in the family came first? Secondly, if it is completely true that all genes came from existing genes, how would one know which gene was the original ancestor of all genes?
Going to watch some astronomy show now. Will blog again later. Evileye | 10:40 PM