What Is Mitochondria?
Mitochondria is a membrane-bound cell organelle, it is found in eukaryotic cells. The primary function of this organelle is to produce ATP (adenosine triphosphate) and hence is called the powerhouse of the cell. Mitochondria are made up of a double membrane which has its own functional importance. The inner membrane is folded and extends into the inner surface of the cell. The Matrix of the organelle contains genetic material and the enzymes that regulate the function of the mitochondria. Mitochondria contain their own genetic system as they are considered to be evolved from the bacteria, they have a similar genetic material which is circular DNA (deoxyribonucleic acid). This mitochondrial genetic material is of great importance as it helps in protein synthesis, translation, and many biological processes.
What Is Human Mitochondrial Genetics?
Human mitochondrial genetics is a science branch that studies and researches human mitochondrial DNA. Human mitochondrial DNA is considered an important variant of hereditary information present in human mitochondria. These studies have gained popularity as the mitochondrial DNA does not follow the Mendelian inheritance pattern (a child receives half of the genetic material from each parent). Mitochondrial DNA is inherited only from a mother in humans, unlike most multicellular organisms. The reason for this type of inheritance is the fertilization process, the sperm discards its contents and mostly only maternal organelles are passed on to the offspring. In some rare cases, it can also be inherited from the father. Mitochondrial DNA codes for 80 percent of the mitochondrial RNA.
How Are Mitochondrial Genes Inherited?
Mitochondrial diseases are inherited maternally and through chromosomal inheritance. The occurrence of the disease and the clinical symptoms completely depend on mitochondrial genetic mutations. These diseases are passed on from generation to generation, and these mutations can occur on any chromosome. Therefore, the inheritance pattern of these diseases varies widely, and mitochondrial diseases can be autosomal dominant, recessive, or sex-linked dominant or recessive based on the chromosome involved in the progression of the disease. As the process of transfer of mitochondrial DNA is complex, it is difficult to find the mutated chromosome. Once mutated, this chromosome affects the production and regulation of other important functional proteins in the mitochondria. These mutations present minor clinical symptoms that help in suspecting the condition. Some mitochondrial mutations are large and severe enough to cause devastating medical symptoms and damage to muscular, neural, and hepatic tissues. The amount of inherited mutant mitochondrial DNA can vary greatly, and no factors can govern or control this transfer of mitochondrial genetic material. It has been observed that the mitochondrial genetic material transferred from mother to child is only the amount available within the fertilized oocyte, ranging from two to ten mitochondrial DNA molecules. Studies suggest that even if the twins do not receive an equal amount of mutated mitochondrial chromosomes, one of the children can have 80 % of the mutated genetic material and will be affected. In contrast, the other will be completely unaffected as the genetic material transferred will be just a few fragments.
Where Are Mitochondrial Genes Located?
Complete human mitochondrial DNA has been mapped, and the research suggests that mitochondrial DNA has two strands: one heavy and one light chain. The light chain of the mitochondrial DNA carries 28 genes, and the heavy chain has nine genes. Human mitochondrial DNA consists of 16,569 nucleotide pairs, and the complete molecule is regulated by one regulatory region. This region is also called the region for the origin of replication.
What Are Mitochondrial Diseases?
Mitochondrial DNA has a variety of proteins, but not all of them are known; the information available so far suggests that most of the mitochondrial proteins are involved in the production of ATP; these proteins being present on the chromosome increases the chances of the mutation and is inherited by the mendelian pattern of inheritance. Some other studies suggest that chromosomal mutation affects specific tissues, especially those that require high energy or have high anabolism or catabolism of a specific nucleic acid. Mitochondrial diseases range in severity and can be completely asymptomatic or fatal. The severity of the disease depends on the severity and degree of mutation. The disease is diagnosed at birth or sometimes even during intrauterine life. The symptoms of these disorders resemble other genetic conditions and are even specific to different individuals therefore it becomes difficult to diagnose. This wide diversity among the symptoms and presentation of the disease is attributed to the presence of several mitochondria in a single cell which have different roles and this characteristic of the mitochondrial cell is called heteroplasmy. The disease is expressed only when a certain tissue reaches a level of mutant mitochondria, the ratio of this mutant mitochondria differs from cell to cell and person to person. Mitochondrial diseases not only cause abnormalities but may also result in mitochondrial dysfunction and result in systemic conditions like diabetes mellitus, cancer, cardiovascular diseases, myopathies, etc. This mitochondrial DNA also plays a role in the process of aging.
What Is the Role of Mitochondrial Genetics in Forensics?
Mitochondrial genetics is widely used in forensic medicine to identify individuals and compare the remains for the identification of missing people with the help of skeletal remnants. Though mitochondrial DNA is not specific to any person it becomes helpful as every cell has plenty of them, which increases the sample size and the actuality of the results presented. Mitochondrial DNA is used along with other anthropological and circumstantial pieces of evidence to identify an individual. It is believed that the use of mitochondrial DNA provides better accuracy in comparison to nuclear DNA when used for the identification of older skeletal remnants, due to its large sample size and the match can be obtained even if maternal generations are separated.
Conclusion
Mitochondria are the cell organelles that contain their own genetic material which is a circular DNA that is present in the cytoplasm of the cell. This DNA is transferred from a mother to the child and follows a non-mendelian inheritance pattern. This mitochondrial genetic material is of great importance as it even helps in identification of the missing or lost individuals. Any mutation in this genetic material, while it is being transferred, can result in abnormalities or diseases, which are commonly termed mitochondrial genetic disorders. These disorders vary in severity and can be diagnosed at various stages of life some during intrauterine life, at birth or even during adulthood. These mutations when are minor lead to systemic abnormalities and result in conditions like diabetes mellitus, Alzheimer's, etc.
