ALMEYDA — I’ll repeat (for the second time in this thread) that it is quite frustrating to find you arguing "no mechanism for additional information" in this thread, after I’ve given you a valid mechanism in another thread, and you gave no refutation of it. I’m reposting here in hopes that I won’t be ignored for a third time.
If there is something you don’t understand in the post, please let me know and I’ll do my best to explain. The basic idea is that mutation accumulation AFTER DUPLICATION can result in two genes with different function, and hence additional genetic information.
I’ll thank you in advance for your reply to this post:
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Almeyda, in another thread writes:
There has been a loss of genetic information, the opposite of what molecules-to-man evolution needs.
I'm sure you'll deny it by your incorrect VCR tape analogy, but duplication and rearrangement at chromosomal and smaller genetic units is a means to increase the "genetic information."
I think your misconception on this point comes from the idea that: if a gene is copied, you'd just have two copies of the same gene, and therefore nothing new would come of it.
If so, you are not thinking about what happens later, as the two copies of the gene accumulate different mutations, and diverge in function. Indeed, evolution predicts that one copy of the gene would be lost if no changes occurred since completely redundant function would leave no selective force to have both copies.
This is why we have what are called "gene families," a simple example being the ERBB receptor family. It has four members, duplicated from a single ancestral ERBB receptor gene, but each member has since changed sequence, and hence function. Thus the receptors' ligand specificities have diverged, as has their downstream signaling pathways. Loss of any one ERBB results in embryonic lethality.
"Lower" organisms like the fruit fly and nematodes have one ERBB gene homologue. Indeed, it is not that humans some how have ‘better’ or novel genes compared to "lower" organisms — but more often that the human genome contains large specialized gene families while "lower" organisms have only one or two types of that gene. Also, complexity not at the gene coding level but in expression of the genes adds much complexity to the human genome.
Also, duplications and rearrangments can "remix" existing genes, coding for hybrid proteins with functions from each of the original proteins. These hybrid genes can accumulate mutations.
Also, duplications/rearrangments can leave gene coding sequence intact, but change regulatory elements associated with the gene, causing it to be expressed in a new tissue site, or at a different level.
So, it is not that every single gene has arisen by chance. Most genes are made up of domains that have similar sequence and produce protein domains with similar function. Thus, only one ancestral kinase domain could have been duplicated to produce the hundreds of different genes containing a kinase domain.
Imagine a gene that codes for a protein with an extracellular domain that attaches to something outside of the cell. Duplication, rearrangment, and now a new hybrid gene exists with an extracellular binding domain and a cytoplasmic kinase domain - a kinase receptor is born...
This kinase receptor can duplicate, rearrange, mutate; and now you have a family of several kinase receptors...
This message has been edited by pink sasquatch, 06-27-2004 09:29 PM
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