Would you expect that humans and other primates would share a gene for vitamin C synthesis? Probably so. Would you expect that gene to be broken in both? Maybe. Would you expect that the changes that break that gene would be an identical viral insert in the same exact place? Not unless you're really credulous--then I have a bridge to sell you!
The similarity in "junk DNA" is more compelling than the similarity in coding DNA from a young-earth point of view, I think. After all, why would God make people and apes with broken genes? If he made them with functioning genes, how did they manage to get broken in the same way? I told another poster that if he could find a way to target one particular sequence out of the billions of bases in our DNA and modify that so specifically, he should get a Nobel prize. There is no known mechanism for inducing this change. Researchers would love to find a way to do this because it would provide a means for genetic engineering and for fighting cancer.
To be honest, I would expect our DNA to be very similar, we look a lot alike! Our hearts and lungs and kidneys probably work in the exact same fashion so I would expect the DNA coding their constrution and DNA coding the proteins that facilitate their use would be indentical.
First, no, Mercury, there is no foot in your mouth.
Interestingly, their function is the same, but their gene sequence is not identical. To digress a bit, this very fact proves problematic for those young earth creationists who say that mutation is always detrimental and always results in loss of specificity. Having a
single exact sequence is not required to retain enzyme activity. Indeed, it's been shown in a variety of species that a protein that is an orthologue (a protein from a different species with the same origin but a slightly different sequence) of one of the creature's own proteins can correct an absence of that protein. Obviously, then, having a slightly different protein sequence is not necessarily going to cause you to keel over and die.
So since having a single exact sequence is not critical, we would expect that on occasion a mutation would arise that does not result in a loss of function for that protein. After a long period of time, we would be able to look at the gene sequence and see that it is significantly different than it was at the beginning. With enough time we might even be able to recognize certain parts of the gene sequence that remain the same because those amino acids are critical for the protein. We would be able to calculate the rate of mutation, and from that we would be able to calculate the time in the past when two populations of that creature were separated and their gene sequences began to diverge.
Interestingly, young earth creationists generally do accept genetic similarity as evidence of relatedness--but only as long as they feel comfortable with the amount of change that has happened. For instance, most young earth creationists think that all of the species alive came from some original kinds that God made, which then evolved and speciated into the species we see now. Thus all maples came from an original maple, all cats came from an original cat, and all doglike canids came from an original doglike canid. These kinds can supposedly be detected by the member species' ability to hybridize within the kind.
Unfortunately apparently all frogs did not come from one original frog, even though most can hybridize, because frogs produce a staggering variety of antimicrobial peptides with different sequences and lengths, which can be specific down to the species level. Since young earth creationists deny the ability of creatures to produce new genes coding for new proteins or peptides, that means that all of these frogs must have come from their own kind--in spite of the evidence that mechanisms such as duplication of existing genes and mutation can result in the production of new proteins or peptides. And again, there must have been multiple original kinds of foxes, since the foxes vary greatly in their number of chromosomes and most are incapable of interbreeding. Once again, this ignores the evidence that chromosome changes such as merging or splitting can result in a decrease or increase in the number of chromosomes, so likely the ancestral fox was capable of interbreeding with other canids. But I digress!
At any rate, I'm sure most educated young earth creationists would agree that dogs are more closely related to wolves than to the other members of the group based upon gene evidence and morphology. But if we can conclude from genetic evidence that dogs are related to wolves, what logical reason can we have for then ignoring other evidence of genetic relatedness because it disagrees with prior assumptions?
I'm going to go ahead and post again some about the evolution of the Volvicide algae and a single cell to multicellular transition:
Chlamydomonas reinharditii are phytoflagellates, tiny unicellular biflagellated photosynthesizing protists. They reproduce asexually (sexual reproduction is present as well, but it is chiefly a method to produce dormant spores to survive difficult times) by multiple fission, in which the cell increases its size 2^n times and then divides n times into 2^n number of daughter cells, n being 2, 8, 4, 16. The daughter cells formed are enclosed inside the mother cell's cell wall, which then bursts to release the daughter cells, which swim off on their own. However, it has been reported on several occasions that the
Chlamydomonas daughter cells do not swim off separately because their cell walls are linked together at points and their cytoplasm is continuous. This produces a little "colony" of
Chlamydomonas cells similar to
Gonium.
Gonium is a colonial biflagellated phytoflagellate occuring in groups of usually 8 or 16 cells. The cells are joined at points and the cytoplasm is continuous among the cells. However, sometimes when cells of the species
Gonium dispersum undergo multiple fission and release the daughter cells, they are unjoined and swim away separately remarkably like
Chlamydomonas. Indeed, genetic studies of
Chlamydomonas and
Gonium show similarities in both coding and noncoding regions (see papers below and
this link), with
Chlamydomonas reinharditii being most closely related to
Gonium, most likely a direct descendant of the original ancestor.
Gonium is a simple colonial organism, and there is no division of labor among the cells. However, there are a variety of more complicated organisms in the same order, Volvocida, that have been shown by genetic testing to be related. The most complicated of these is
Volvox, a colonial organism in which some thousands of somatic cells in a globe surround germ cells on the inside of the colony. Asexual reproduction in
Volvox involves multiple fission of one of the germ cells to produce a tiny daughter colony. The somatic cells undergo programmed cell death at only four days old, releasing the daughter colonies.
While
Gonium is a flattened disc, all of the other Volvocida members are globular. This is important because the initial colony embryos have the flagella pointing in towards the center of the globe, making them useless for locomotion. In order to function, they must invert. This inversion is carried out by the action of InvA, a novel kinesin, which acts on the microtubules at the cytoplasmic bridges to bend the sheet of cells. This protein is required in
Gonium as well, where it switches the concavity of the colony so that the flagella are on the convex side. InvA is coded for by the gene
invA.
Chlamydomonas,
Gonium,
Pandorina,
Eudorina, and
Pleodorina all have a gene that is a orthologue of
invA, and the gene in
Chlamydomonas, IAR1, has been inserted into an inversion-incapable
invA Volvox mutant, enabling inversion. This is yet another instance of novel use of a pre-existing protein (also demonstrated in another case by the ability of the
Chlamydomonas orthologue of
gls to return asymmetric cell division to a
Volvox gls mutant).
The next major hurdle after cytoplasmic continuity and embryonic inversion is germ-stroma division of labor in
Volvox. This is caused by two gene expression regulators,
regA, which represses chloroplast protein synthesis in somatic cells (required for germ cells to pass on chloroplasts, stalling the usual transition from biflagellated stage to nonflagellated reproductive stage), and
lag, which keeps germ cells from developing somatic features like flagella and eyespots. It currently is unclear whether these genes are new inventions in Volvox or if they are present in ancestors but not used for this purpose.
The close genetic and morphological similarity among the Volvocida members show that they have a common ancestry and are closely related. The genetic and morphological similarity between
Chlamydomonas reinharditii and
Gonium show that these two have a relatively recent common ancestor. This demonstrates an evolution from a single-celled "lifestyle" to a multicellular colonial one.
Coleman A. W.; Mai, J. C. "Ribosomal DNA ITS-1 andITS-2 sequence comparisons as a tool for predicting genetic relatedness."
J Mol. Evol. 1997, 45:168–177.
Kirk, David L. "Volvox as a Model System for Studying the Ontogeny and Phylogeny of Multicellularity and Cellular Division."
J. Plant Growth Regul. 2000, 19:265-274.
Kirk, David L. "Seeking the Ultimate and Proximal Causes of Volvox Multicellularity and Cellular Division."
Integ. Comp. Biol. 2003, 43:247-253.
Cole, Douglas; Reedy, Mark. "Algal Morphogenesis: How
Volvox Turns Itself Inside-Out."
Current Biol. 2003, 13:R770-R772.
Kirk, David L. "A twelve-step program for evolving multicellularity and a divsiton of labor."
BioEssays 2005, 27:299-310.
Liss, Michael; Kirk, David; Beyser, K.; Fabry, S. "Intron sequences provide a tool for high-resolution phylogenetic analysis of Volvocine algae."
Curr. Genet. 1997, 31:214-227.
Nozaki, H.; Itoh, R.; Sano, H.; Uchida, M.; Watanabe, M.; Kuroiwa, T. "Phylogentic relationships within the colonial Volvocales (Chlorophyta) inferred from rbcL gene sequence data."
J. Phycol. 1995, 31:970-979.
