Genetic Similarities

I'm curious about genetic similarities between all life on earth (including plants and animals). For me one of the most convincing reasons to believe in evolution would be similarities in the genetic code of animals that currently look similar, and as similarity decreased, so would the genetic code. This is explained by evolution because from a common ancestor, genetic mutations would become different over time. Most of the differences would occur in DNA that wasn't essential to the survival of the species (it's easier to tinker with non-essential aspects of a system).Essential systems, however, over time should remain relatively constant. I remember reading somewhere (i can't remember exactly) that cows and pea plants (including all other life on earth) share a common sequence of DNA that codes for the splitting of mitochondria.I'm almost positive my above example is wrong in some way, so i was wondering if someone could correct my example. Is there a sequence of DNA that is found in most (if not all) life on earth that codes for a specific process that we know about?Creationists talk about how no matter how many times dogs have offspring, the offspring will always be dogs. They also comment that regardless of how similar the genetic code between chimps and humans are different "kinds". my second question is what are the respective genetic differences between very dissimilar dogs (lets say st. bernards and chihuahuas... but i'll take anything really) and chimps and humans?I think creationists would predict the genetic differences in dogs (the same kind) would be LESS than the genetic differences in chimps and humans (different kinds).unless they see no correlation at all between genetic code and kinds... but i would still like to know the answer.[This message has been edited by TheoMorphic, 10-28-2003]

From what I have learnt from my books,
1. ALL humans' DNA is similar to one another by 99.9%.
2. Human's DNA is similar to a mammal (pig) by 99%
3. Human's DNA is similar to a housefly by 90%What does the above imply?

I'm not sure that those statistics are exactly correct, but it's far more compelling then just overall similarity: It is the issue of exact or near exact sequences being maintained. For example, substituting words for genes, if we had species with the following genotypes:The Quick Brown Fox Jumped Over The Lazy Dogs
The Quick Brown Horse Jumped Over The Lazy Lions.
The Mean Brown Horse Hopped Over The Happy Lions.
The Slow Brown Horse Hopped Over The Happy Lions
The Quick Red Horse Hopped Over The Happy Lions
That Quick Brown Horse Hopped Over The Happy Lions.
That Quick Red Horse Hopped Under The Happy Lions.You will never find:That Quick Red Fox Jumped Under The Lazy DogsThe genes "That", "Red", and "Under" evolved on a completely different lineage than "Fox", "Jumped", and "Dogs" did. In a real-world situation, there are *many, many* genes to compare to, and the case becomes incredibly compelling once you start getting up into thousands of genes. Occasionally there are minor exceptions (convergent evolution of particular, highly mutable genes from species put in very similar niches, although exact convergence is almost never found), but the genotype as a whole displays this stark pattern to an amazing degree.Also, you can get a glimpse at the common ancestor - in this case, the common ancestor probably had genes that looked like:The Quick Brown Horse Hopped Over The Happy Lions.------------------
"Illuminant light,
illuminate me."

i'm looking more for a specific example. is there an essential sequence of genetic material that all (or most) life has in common (maybe not exactly the same, but significantly similar)? does this sequence code for something so essential that a minor change does not allow the organism to develop into reproductive maturity?

I'm guessing that even St Bernards and chihuahuas are more similar in DNA sequence than humans and chimps, but I have no data to back that up. I have, however, seen a study (the paper is at home - link tonight) that shows a couple of mice - different species of the genus Mus - that are considerably more different over 12,000 genes than are chimps and people.

A biochem book that I have borrowed (I never had a biochem course!) shows that histone H4 changes 30 times more slowly after species branching events than does cytochrome C, and 100 times more slowly than hemoglobin. So plant and animal histone is very nearly identical - 3%, maybe, difference in amino acids. Cytochrome C is more like 45% different. Is this more like what you're after?Re my post above: Enard, et al., Science, 296, pp 340-343, (2002). It's online with free registration at Science | AAAS
Their data, along with some they quote, has humans 1.08% divergent in some measure of our DNA from chimps, and 2.98% from orangutans. The common house mouse, Mus musculus, is 2.5% different from M. spretus and 4.5 from M. caroli.
The article is actually about how gene expression is very different in human vs. other ape brains, which may be why we (claim to be/are) smarter than them. It's worth a read.

Do you mean a specific gene or a type of gene? The distinction is important as polymerases exist in all phyla but have duplicated, diverged, been eliminated, changed function etc.Here is an example of a extremely widely distributed class of proteinsGene. 2001 Jun 13;271(1):81-6. Related Articles, LinksMolecular characterization of homologues of both subunits A (SPO11) and B of the archaebacterial topoisomerase 6 in plants.Hartung F, Puchta H.Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, D-06466 Gatersleben, Germany.The Spo11 protein is an eukaryotic homologue of the topoisomerase 6 subunit A from archaebacteria. In yeast Spo11p has been found to bind covalently to double-strand breaks (DSBs) during meiosis. Single homologues of the SPO11 gene exist in various eukaryotes, except plants. Previously, we found in the Arabidopsis thaliana genome two ancient paralogs, AtSPO11-1 and 2. Here we report on the molecular characterization of a third one, AtSPO11-3. This puzzling finding might be explained by the fact that we detected additionally--for the first time outside of the archaebacterial kingdom--a homologue of the subunit B of topoisomerase 6, AtTOP6B. Both AtSPO11-3 and AtTOP6B are abundantly expressed in Arabidopsis and EST comparisons indicate the presence of both genes in various plant species. Via two hybrid studies we could demonstrate that full length AtTop6B is able to interact with AtSpo11-2 and 3 but not with AtSpo11-1. Our data suggest that plants possess in contrast to other eukaryotes an additional archaebacterial kind of topoisomerase.

holy crap dude... that was over on the brad mcfall side of the incomprehensibility scale.by example i mean "So there is a sequence of DNA that codes for Operation X. Every organism on earth has to perform Operation X at some point in their life. Humans have this sequence that codes for Operation X, and so does this boot scum that i found in my closet (on my boot)."call me lazy (in that I would prefer to not have to do extensive research in biochemistry and genetics to understand the example) but understanding calculus (actually understanding it, not just going through the motions) is taking up enough of my time right now.

Hmm...must be slipping if I sound like Brad now...Ok simple examples, DNA polymerases, topoisomerases, DNA repair enzymes, helicases...genes all necessary for DNA based life, genes present in your boot scum (ever consider cleaning your closet?) all the way up to McFall.

Here is a very informayive article on species-species sequencing. It includes (near the bottom a table of Cytochrome-C sequences showing percentage differeneces, and also shows hopw the data is interpreted - and how creationists mis-interpret it.