Multiple Choice
Which of the following would occur if an Alu element jumped into the AG splice site of a human gene?
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16. Transposable Elements
Transposable Elements in Eukaryotes
0:51 minutesProblem 21
Textbook 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?
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Understand the role of transposons: Transposons, such as Ds (Dissociation) and Ac (Activator) elements, are mobile genetic elements that can move within the genome. Their insertion into or near a gene can disrupt its function, leading to a mutant phenotype.
Consider the reversion of the mutant phenotype: When a transposon transposes away from its original insertion site, the gene's function may be restored, leading to a reversion of the mutant phenotype. This occurs because the disruption caused by the transposon is removed.
Analyze the possibility of more severe phenotypes: In some cases, the transposon may cause additional mutations during its movement. For example, it might leave behind a footprint (small sequence changes) at the original site or insert into another critical region of the genome, further disrupting gene function.
Examine the effects of transposon activity on nearby genes: The transposon may also affect regulatory elements or neighboring genes. For instance, it could alter the expression levels of nearby genes by disrupting enhancers, silencers, or promoters, leading to more severe phenotypes.
Consider chromosomal rearrangements: Transposon activity can sometimes lead to larger-scale genomic changes, such as deletions, duplications, or inversions, at or near the site of transposon insertion. These structural changes can exacerbate the mutant phenotype by affecting multiple genes or regulatory regions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Transposons
Transposons, or 'jumping genes,' are DNA sequences that can change their position within the genome. They can disrupt gene function by inserting themselves into or near genes, leading to mutations. In maize, the Ds and Ac transposons are known for their ability to transpose, which can result in phenotypic changes, including reversion to wild-type traits or the emergence of new mutations.
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Gene Regulation
Gene regulation refers to the mechanisms that control the expression of genes, determining when and how much of a gene product is made. Transposons can influence gene regulation by inserting into regulatory regions or altering chromatin structure, potentially leading to increased or decreased expression of nearby genes. This can result in unexpected phenotypes, including more severe mutations.
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Mutagenesis
Mutagenesis is the process by which genetic information is changed, resulting in mutations. In the context of transposons, they can cause mutagenesis by inserting into functional genes or regulatory elements, leading to loss of function or gain of function mutations. The severity of the resulting phenotype can vary based on the nature of the mutation and its impact on gene function.
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