Visual communication aid: Mitochondrial inheritance

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• Mitochondrial inheritance

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We all have over 20,000 genes, which provide instructions for how our body works. Genes are made of DNA. Most genes are found inside the nucleus of a cell, known as nuclear DNA. Some genes are found in the mitochondria of a cell.

Mitochondria are structures found inside most cells in the body. Their job is to produce energy the cell needs. Each mitochondrion inside a cell contains a copy of a person’s mitochondrial DNA (figure 1).​

Changes in mitochondrial genes can cause genetic disease. Usually, a person will have some mitochondria with the gene change and some without the gene change.

Figure 1: Human cell showing nuclear DNA and mitochondria

Genes in the mitochondria are always inherited from the mother. Mothers will pass a random selection of their mitochondria on to their children. If a mother carries a mitochondrial gene change, this will be inherited by their children.​

The severity of a condition will depend on the number of mitochondria with a gene change someone inherits. Some people with very low numbers of mitochondria may have milder symptoms, or no symptoms at all.​

Both males and females can inherit a mitochondrial gene change from their mother, but males will not pass this on to their children because sperm cells do not contribute any mitochondria at conception (figure 2).​

Figure 2: Diagram showing how changes in mitochondrial DNA are inherited
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• Nuclear DNA: DNA found inside the nucleus of a cell​.
• Mitochondrial DNA: DNA found inside the mitochondria of a cell.
• Gene change: Changes in a gene used to be referred to as ‘mutations’. Now, they are more commonly called changes, alterations or variants.