16. Transposable Elements

Transposable Elements in Eukaryotes

Open Question
In maize, a Ds or Ac transposon can alter the function of genes at or near the site of transposon insertion. It is possible for these elements to transpose away from their original insertion site, causing a reversion of the mutant phenotype. In some cases, however, even more severe phenotypes appear, due to events at or near the mutant allele. What might be happening to the transposon or the nearby gene to create more severe mutations?
Multiple Choice
Which of the following is true regarding reverse transcriptase?
Multiple Choice
Which of the following elements is a transposable element in Drosophila?
Multiple Choice
Which of the following is an example of a safe haven for transposon movement?
Multiple Choice
Which of the following would occur if an Alu element jumped into the AG splice site of a human gene?
Open Question
The human genome contains a large number of pseudogenes. How would you distinguish whether a particular sequence encodes a gene or a pseudogene? How do pseudogenes arise?
Open Question
Contrast the structure of SINE and LINE DNA sequences. Why are LINEs referred to as retrotransposons?
Open Question
Compare DNA transposons and retrotransposons. What properties do they share?
Open Question
It is estimated that about 0.2 percent of human mutations are due to TE insertions, and a much higher degree of mutational damage is known to occur in some other organisms. In what way might a TE insertion contribute positively to evolution?
Open Question
The human genome contains approximately 10⁶ copies of an Alu sequence, one of the best-studied classes of short interspersed elements (SINEs), per haploid genome. Individual Alu units share a 282-nucleotide consensus sequence followed by a 3'-adenine-rich tail region [Schmid (1998)]. Given that there are approximately 3 x 10⁹ base pairs per human haploid genome, about how many base pairs are spaced between each Alu sequence?
Open Question
It has been noted that most transposons in humans and other organisms are located in noncoding regions of the genome—regions such as introns, pseudogenes, and stretches of particular types of repetitive DNA. There are several ways to interpret this observation. Describe two possible interpretations. Which interpretation do you favor? Why?