June 24, 2009

• DNA transposons without the religious dogma of the evolutionist .

   “DNA transposons, or ‘class II transposable elements’, move from place to place by replicative transposition (that increases the copy number) or by a simple cut-and-paste mechanism. Though in general not as common or in as high a copy number as retroelements, they are still found in most organisms. Examples are the Drosophila P elements, bacterial transposons such as Tn10 and Tn7, the Mu phage, and the ubiquitous mariner/Tc1 superfamily of transposons. The mariner/Tc1 family is the most widespread, being found in most insects, flatworms, nematodes, arthropods, ciliated protozoa, fungi and many vertebrates, including zebra fish, trout and humans. Copy number varies from two copies in Drosophila sechellia, to 17,000 in the horn fly Haematobia irritans, accounting for 1% of the genome. The vast majority of them appear to have been inactivated by multiple mutations. The close homology between mariner/Tc1 elements found in species thought to have diverged 200 million years ago has fueled the hypothesis that these elements can transfer horizontally (that is, not by normal inheritance) between different species, or even different phyla (see below). Again, the evolutionist gets to pick and choose from his smorgasbord of explanations when the data do not fit the evolutionary tree.

  Miniature inverted-repeat transposable elements (MITEs)

  A recently discovered third class of mobile elements is the miniature inverted-repeat transposable elements (MITEs). They are very small (125–500 bp), and have short terminal inverted repeats. They were first found in plants, but have also been found in nematodes, humans, mosquitoes and zebrafish. They are found in the thousands and tens of thousands per genome, and have been given colorful names (e.g. Tourist, Stowaway, Alien and Bigfoot) to reflect their apparent ability to move about in the genome. Their mechanism of transposition is still unknown, but they appear to be DNA elements that cannot move about on their own (non-autonomous). Though none seem to be presently active, they are believed to have been mobile in the recent past because of the high levels of sequence similarity between elements in a particular family, and the differences in insertion sites seen in closely related species.  MITEs are particularly interesting in terms of generating genetic variation in that they are preferentially associated with genes.

  Effects of mobile and repetitive elements on gene expression

  Mobile elements and repetitive elements can alter the structure and regulate expression of the genome in several different ways. As described earlier, transposition can disrupt genes by direct insertional mutagenesis and can adversely affect transcription. Many retrotransposons have strong constitutive (always on) promoters that can cause inappropriate expression of downstream genes. If the promoter is in the opposite direction of the gene, RNA complementary to the mRNA of the gene can be made that can act as antisense RNA  that binds up the mRNA, affecting translation.

  Recombination between similar DNA strands is a necessary process for repair of DNA breaks and allele  shuffling between homologous chromosomes. But the presence of mobile and repetitive elements in inappropriate positions can result in recombination products that are deleterious, such as translocations , inversions , and other chromosomal rearrangements (Figure 5). For example, it was shown that a widespread chromosomal inversion commonly seen in Drosophila buzzatii is caused by the recombination between two copies of a transposable element in opposite orientations.  There can even be an exchange of DNA between non-homologous chromosomes: such as was seen in maize, in this case mediated by the recombination of one complete and one partial copy of the Ac (Activator) transposable element.

  Figure 5. Recombination between direct repeats causes the loss of the DNA between them.”

  

  For more of where this came from go to http://creation.com/junk-dna-evolutionary-discards-or-gods-tools

  Barry

  • 11:30 pm
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