Which of the following statements about mobile (aka repetitive type) genetic elements is FALSE? A. Movement of a mobile genetic element can change the phenotype of an organism, usually by causing insertional mutagenesis. B. Retrotransposons include LINE and SINE type sequences. C. Mobile genetic elements may have no biological function for the organism; it is possible that their only purpose is to propagate themselves. D. The movement of the corn Ds element is an example of a ‘cut and paste’ type mechanism. E. An ‘autonomous’ mobile genetic element is one that requires components produced by ‘nonautonomous’ elements (such as reverse transcriptase) in order to move.
The correct answer and explanation is:
Correct Answer: E. An ‘autonomous’ mobile genetic element is one that requires components produced by ‘nonautonomous’ elements (such as reverse transcriptase) in order to move.
This statement is false. In fact, the opposite is true. An autonomous mobile genetic element is capable of moving on its own because it carries all the necessary components, such as genes that encode enzymes like transposase or reverse transcriptase, which are required for its movement. In contrast, a nonautonomous element lacks some or all of the genes necessary for mobility and thus depends on enzymes produced by autonomous elements to move within the genome.
Mobile genetic elements, often called transposable elements or “jumping genes”, are DNA sequences that can change their position within the genome. Their movement can have various effects on an organism. For example, if a transposable element inserts itself into a functional gene, it can disrupt that gene’s function. This is known as insertional mutagenesis, and it can lead to phenotypic changes.
There are two primary classes of transposable elements: DNA transposons, which typically move through a cut-and-paste mechanism, and retrotransposons, which move through a copy-and-paste mechanism involving an RNA intermediate. Retrotransposons include LINEs (Long Interspersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements), which are common in eukaryotic genomes and particularly abundant in the human genome.
The Ds element in corn is a classic example of a nonautonomous DNA transposon that requires the Ac element, an autonomous transposon, to provide the transposase enzyme for its movement. This process uses the cut-and-paste method.
Therefore, all the other options (A, B, C, and D) are true, and only option E contains a false statement about mobile genetic elements.