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Which of the following is not true about transposable elements?
Transposable elements are portions of the DNA that are free to move around the genome and are generally considered non-coding DNA. This can be potentially dangerous, however. Transposable elements can insert themselves in the coding regions of genes, thus making them non-functional. This can lead to disease. Both eukaryotic and prokaryotic genomes contain transposable elements.
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Transposable elements, or transposons, are separated into two classes. Which of these categories of life have class I transposons in their genomes?
I. Bacteria
II. Yeast
III. Eukaryotes
Class I transposable elements are RNA-mediated elements of a single evolutionary origin, and are found in yeast, which only have class I elements, and in eukaryotes, which have both class I and class II elements. Bacteria only have class II elements, and hence are not included in the correct answer to this question.
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Barbara McClintock initially discovered transposons in her work on corn at Cold Spring Harbor Lab, which she called the Ac / Ds system. What were dissociators (Ds)?
Barbara McClintock named the transposons that are defective, and serve as sites of chromosomal breakage where other transposons insert (the associator, Ac) the dissociators. These were likely transposons that lacked the transposase that catalyzes their movement.
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Transposable elements can be significant factors in causing newly resistant bacterial strains. How do transposons cause resistance to develop?
Two transposons flanking an antibiotic resistance gene can easily move between bacteria and confer new resistance. A mix of transposons and new genes such as this is called a composite transposon. Recall that bacteria exchange genetic information via conjugation, transduction, and transformation.
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What makes an LTR retrotransposon unique among other transposons?
LTR stands for Long Terminal Repeats, which are 250-500 base pair repeats located on the ends of a transposon. These repeats encode a series of proteins, most significantly transposase. These are very likely to be early evolutionarily stages of retroviruses.
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How do non-LTR retrotransposons insert into the genome?
Non-LTR retrotransposons use an endonuclease that nicks thymine-rich host DNA, which eventually leads to incorporation of the transposon by host DNA repair functions. These other methods are all associated with different specializations of transposon.
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What differentiates a LTR retrotransposon and a retrovirus?
The only difference between most LTR retrotransposons and retroviruses are that retroviruses can encode an envelope protein. Phylogenetic analyses have shown that retrotransposons and retroviruses are extremely closely related, and may be direct ancestors of one another.
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The hybrid dysgenesis phenomenon was observed in Drosophila flies. It was determined that this was caused by a transposon no longer under control in wild type - lab strain crosses. What are transposons commonly controlled by in their hosts?
Movement of transposons is very commonly controlled by RNA interference. The RNAi system cuts up problematic RNAs, and uses these small pieces to target transposons for destruction.
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How do transposons rapidly propogate through and between species?
It is hypothesized that transposons can rapidly move through populations and species by horizontal transfer, most likely through viruses.
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