Question at position 22 Alterations to DNA sites such as promoters and operators can actonly in trans.These terms apply only to posttranscriptional regulation.only in cis.either in trans or in cis.Clear my selection

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Restating the question and options to set the stage: Alterations to DNA sites such as promoters and operators can act only in cis. Which of the following statements matches this idea?

Option 1: 'only in trans.' This is incorrect because changes to DNA sequence that are located on the same DNA molecule typically affect that molecule directly (in cis) rather than acting as diffusible factors elsewhere (in trans). Trans refers to diffusible products (like transcription factors) acting on DNA, not the DNA change itself.

Option 2: 'These terms apply only to posttranscriptional regulation.' This is inaccurate; cis/trans terminology describes the relationship between DNA elements and the genes they regulate, which is a DNA-level (often transcriptional) concept, not limited to posttranscriptional regulation.

Option 3: 'only in cis.' This statement aligns with the standard meaning: alterations to DNA elements such as promoters and operators influence only the same DNA molecule (in cis), not other molecules unless the same regulatory elements or factors are provided in trans.

Option 4: 'either in trans or in cis.' While some regulatory effects can involve trans-acting factors, the specific claim that alterations to DNA sites can act both in trans and in cis is misleading for the DNA element itself, which acts in cis. The distinction is about the location of the effect relative to the DNA: cis effects occur on the same molecule, whereas trans effects involve diffusible factors acting on multiple molecules.

In summary, the most precise and accurate option is the one stating 'only in cis.', as DNA-site alterations directly influence the same DNA molecule without requiring a diffusible mediator to act on a separate molecule.

Question at position 22 Alterations to DNA sites such as promoters and operators can actonly in trans.These terms apply only to posttranscriptional regulation.only in cis.either in trans or in cis.Clear my selection

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