Pedigree analysis · USMLE Step 1

Which pattern on a pedigree might suggest mitochondrial inheritance?

Affected mothers pass it to all offspring; fathers pass to none
Male-to-male transmission is seen in every generation
The trait is expressed only among the male relatives
Both sexes transmit it equally, regardless of parent sex

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Correct answer: Affected mothers pass it to all offspring; fathers pass to none

Mitochondrial DNA is maternally inherited: an affected mother transmits the trait to all her children, while affected fathers transmit it to none. This maternal pattern is distinctive on a pedigree.

Difficulty: Medium Question 13 of 19

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