Mitochondrial inheritance · USMLE Step 1

Why does mitochondrial inheritance behave as a single locus rather than following Mendelian segregation rules?

  1. Because mtDNA recombines before it is inherited
  2. Because mtDNA is inherited clonally in high copy number
  3. Because mtDNA forms part of the nuclear genome itself
  4. Because paternal mtDNA complements the maternal mtDNA
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Correct answer: Because mtDNA is inherited clonally in high copy number

Mitochondrial DNA is transmitted in multiple copies from the mother’s oocyte and does not recombine; all copies inherited go together, so it behaves as a single non-Mendelian locus.

Difficulty: Medium Question 13 of 19

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