Here's why:

* Mitochondria have their own DNA: Mitochondria, the powerhouses of our cells, have their own small circular DNA called mitochondrial DNA (mtDNA).

* mtDNA is inherited maternally: During fertilization, the sperm contributes only its nucleus (containing nuclear DNA) to the egg. The egg, however, provides the cytoplasm, including the mitochondria.

* Limited paternal mtDNA contribution: While there have been some reports of paternal mtDNA being passed on, it's extremely rare and typically doesn't persist for long in the offspring.

Therefore, almost all the mitochondria you inherit come from your mother, making mitochondrial DNA a valuable tool for tracing maternal lineage.