In the world of science, genetics play a huge role in the way humans develop and evolve, even answering the question of human origin. Dr. Jonathan Coren associate professor of biology presented his lecture, titled “Where Do We Come From?: Tracing Genetic Heritage through Mitochondrial DNA” Tuesday evening, Nov. 12. His presentation was part of the International Education Week celebrated by the College. Coren’s area of study focuses on the origin of genetic heritage by studying mitochondrial DNA and its changes to study the start of human life and existence and our relations to one another on a genetic level.
The start of human life begins with the offspring cell. “In the nucleus, the DNA comes from both parents,” Coren said. “The mitochondrion DNA comes from the mother and is passed from mother to child.” Over 100,000 mitochondrial cells make up the genetic material used to form a person’s genetic makeup. Hundreds of copies of mitochondria exist from our mother in each cell. The genome itself is made up of 37 genes that are responsible for the process of energy conversion through adenosine triphosphate (ATP), a substance present in all living cells that helps to provide energy for metabolic processes and takes part in forming ribonucleic acids (RNA).
During the creation of mitochondrial genes, the process can go awry and people can suffer genetic mutations that cause genetic disorders. “Mostly the mutations in these genes affect the tissues with the highest energy requirements, such as the nervous system, muscles, liver and kidneys,” Coren said. A few disorders that he listed were Kearns-Sayre syndrome, leber optic atrophy, leigh syndrome, MELAS syndrome, MERRF syndrome and progressive external ophthalmoplegia. Coren showed a video of a boy suffering from MELAS, which caused him to suffer from strokes.
Mitochondrial DNA has a few “rules of inheritance,” Coren said. “A mother’s egg contains over 100,000 mitochondria and are passed down in a maternal lineage,” Coren said. “In addition, mtDNA remains unmixed because it only comes from the mother, following a strict line of descent from mother to child.” Mitochondrial DNA can help to trace genetic patterns back to the earliest humans. “We know that modern man evolved in North Africa,” Coren said. “We know it was about 100,000 to 150,000 years ago.” One of the hypotheses for the spread of the human race is the “out of Africa” theory. This theory states that the human population spread out over the globe resulted from a single population that left Africa over 60,000 to 70,000 years ago. Populations spread from Northern Africa to Eurasia, India, Southeast Asia and Australia, eventually moving to colonize North Asia, Europe and beyond.
Using mtDNA, inheritance can be tracked back to the mitochondrial Eve, the maternal ancestor of all living humans. From archaeological findings in bones and skulls, mtDNA can be recovered from the bone. “Because the mitochondrial genome is quite small and abundant, scientists have been able to extract it from bones from thousands of years ago, depending on the conditions,” Coren said. “There are a lot of ancient DNAs that have been identified. This helps the process of identifying current DNA patterns.” Variations in DNA can be used to generate a “molecular clock” that measures the number of mutations over time to estimate evolutionary time. For example, humans and chimps diverged genetically five to six million years ago. This was determined by dividing the number of nucleotide differences by the time that the species divided to give a value of mutations per year. In general, mitochondrial clocks can be about 90 percent accurate.
In addition, ancestry can be determined by looking at a person’s individual DNA samples. Ancestral markers are mutations that occur in the mitochondrial DNA. Makeup of DNA consists of adenine (A), thymine (T), cytosine (C) and guanine (G) pairings. Variations, or mutations from one base to one of the other three bases are common and create unique patterns in an individual’s DNA structure. Humans can use their unique sets of DNA to determine ancestry from thousands of years ago. “Once a mutation occurs, it is passed down to all of its descendants,” Coren said. These common genetic variations, also known as single nucleotide polymorphisms (SNPs), can be cross-examined with other sets of DNA to determine relationships between people. The number of related SNPs between people determines this relatedness. The fewer differences in DNA people have, the greater the relatedness. During the lecture, students compared their own sets of DNA to determine how genetically similarly each student was to another, offering a truly hands-on learning experience.