Mitochondrial inheritance
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What it means
Genes on mitochondrial DNA — maternal transmission only (sperm mitochondria don't contribute); all children of an affected mother may be affected; heteroplasmy → variable severity (threshold effect). Examples: LHON, MELAS, MERRF, mitochondrial diabetes & deafness, Leigh syndrome.
Worked example
A trait passed only through the mother to all her children of both sexes, never through the father → mitochondrial.
In the exam
A disorder of energy-demanding tissues is transmitted exclusively from the mother to all her children; affected fathers never pass it on.
What settles it
Mitochondrial = maternal-only, all offspring at risk; X-linked recessive can come through carrier mothers too but spares father-to-son and has affected males/carrier females.
Classically confused with
X-linked recessive
Source: StatPearls