By Emily Schleicher, 1st year PhD candidate in the Biomedical Sciences Graduate Program
What is the Mitochondrial Genome?
When referring to the genome, most people think of 46 chromosomes, 23 from mom and 23 from dad. The chromosomes are made of DNA,specifically DNA within the nucleus of our cells, and they encode for nearly 25,000 genes that make us who we are. However, what is often neglected is a second genome that is passed directly from mother to child, the mitochondrial genome. The mitochondrial genome resides outside the nucleus in mitochondria, which are found in all eukaryotes and are essential for generating ATP— the energy the cell needs to survive. The mitochondrial genome consists of just 37 genes that encode 13 proteins1. The proteins are mostly enzymes that facilitate the production of ATP, which means they are essential. Just as mutated genes in the nucleus can lead to illness, diseases can arise from mutations in mitochondrial DNA2. These mutations can lead to problems involving muscles, the endocrine system, nerves, brain, heart, and liver, and many can be fatal in the first few years of life. At this point in time, there is no treatment for mitochondrial diseases, but it has become a growing area of biological research in recent years1.
How is the Mitochondrial Genome Inherited?
When sperm and egg meet, both the sperm and egg carry nuclear chromosomes, which is why people inherit genes from both mother and father, but the sperm does not carry inheritable mitochondria. Mitochondria that powers the sperm is located in a portion of sperm that is lost at fertilization. This means that the egg’s mitochondria are all the child will inherit; the effect is that the mitochondrial genome is passed exclusively from mother to child.