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What We Talk About When We Talk About "Junk DNA".

Nelson J R Fagundes1,2, Rafael Bisso-Machado1, Pedro I C C Figueiredo1

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Summary

The concept of "Junk DNA" persists despite identified functions. This study proposes refining the definition by distinguishing between horizontal (ecological) and vertical (temporal) dimensions, introducing "Spam DNA" for elements persisting without selection.

Keywords:
biological functionexaptationgenome evolutionpositive selectionpurifying selectionspam DNA

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Area of Science:

  • Genomics
  • Evolutionary Biology
  • Molecular Biology

Background:

  • The term "Junk DNA" implies non-functional genomic sequences, but many such elements now have identified biochemical functions.
  • This challenges the traditional view, prompting re-evaluation of the "Junk DNA" concept in light of new discoveries.

Purpose of the Study:

  • To refine the definition of "Junk DNA" by addressing the concept of biological function.
  • To introduce a new term, "Spam DNA", to describe genomic elements that persist over time without active selection.
  • To differentiate between the ecological (horizontal) and temporal (vertical) dimensions of genomic element function.

Main Methods:

  • Conceptual analysis of biological function and its relation to evolutionary selection.
  • Distinction between horizontal (ecological) and vertical (temporal) dimensions of genomic elements.
  • Proposal of new terminology to clarify discussions on non-coding DNA.

Main Results:

  • The interpretation that identified functions invalidate "Junk DNA" relies on an incomplete definition of biological function.
  • Genomic elements can persist due to factors other than direct selection for their current role.
  • A distinction is made between "Junk DNA" (no current fitness benefit) and "Spam DNA" (persistence without selection).

Conclusions:

  • "Junk DNA" should be understood in the context of current ecological fitness (horizontal dimension).
  • "Spam DNA" describes elements persisting vertically through time, irrespective of their origin or selection.
  • These concepts are complementary and can explain phenomena like exaptation and constructive neutral evolution.