ancestry – BioQuakes

Evolving from free-swimming bacteria engulfed by forms of humans’ earliest ancestors billions of years ago, almost every human cell is powered by mitochondria, which use oxygen to create usable energy for our body’s daily needs. Originating from free-floating bacteria, mitochondria have unique DNA different from the 23 pairs of chromosomes in our body. Although our chromosomes come from both parents, 23 each, nearly all humans’ mitochondrial DNA (mtDNA) comes from the mother’s egg. What about the mtDNA in the sperm cell then?

Scientists figure that sperm’s mitochondria are soon broken down by molecular processes after fertilization in other animals, but the reason behind why this happens to humans has been unknown. Now research has found that human sperm’s few mitochondria contain virtually no DNA at all. This mtDNA elimination process might play a role in human infertility and mitochondrial diseases, according to molecular biologist Dmitry Temiakov of Thomas Jefferson University in Philadelphia. Coming up with the same conclusion, Shoukhrat Mitalipov, Ph.D., director of the Center for Embryonic Cell and Gene Therapy at OHSU, said, “We found that each sperm cell does bring 100 or so mitochondria as organelles when it fertilizes an egg, but there is no mtDNA in them.” Using molecular biology, researchers found that sperm’s mitochondria did contain some DNA, along with an important protein called mitochondrial transcription factor A (TFAM) that acts to protect that DNA. But after the sperm cells mature, chemical changes happen which prevent TFAM from entering mitochondria, and as it enters the nucleus instead, it no longer prevents the mtDNA from degrading. The fact that DNA damage in sperm from oxidative stress is common could be another reason why mitochondrial DNA disintegrates. Having mitochondrial DNA doesn’t help fertility either; if the sperm’s mitochondrial DNA sticks, it could become a source of infertility. Previous studies showed that sperm cells with elevated amounts of mtDNA experience decreased sperm counts and motility. A new study found that other animals “show multiple mechanisms that may contribute to maternal mitochondrial inheritance in different organisms,” said Xinnan Wang, a mitochondrial cell biologist at the Stanford University School of Medicine. This study connects to our lesson in AP Biology on the concept of genetics and how our DNA is passed on from our parents. Specifically, we previously learned how our mitochondrial DNA is almost completely from our mother, as the egg contains way more mitochondrial DNA than the sperm, allowing us to track ancestry by maternal mitochondrial DNA. This study expands our understanding of this concept. According to Temiakov, there are probably other unidentified mechanisms in sperm cells that regulate mtDNA, as a future area for research as it is crucial to better understand mitochondrial diseases and how to treat them. What do you think would happen if the mtDNA is passed on equally from both parents?

Over the past five years or so, ancestry and DNA tests have risen in popularity due to people’s desire to find out what medical conditions they are at risk for, or where their ancestors are from. The most common concern I have heard about as a result of these tests was that the companies would sell your DNA to third parties or the government (while there is a chance this could be true this will not be the focus of this article). However, the true problems are not conspiracy driven, yet they are scientifically driven and verifiably true.

23andMe is one of the most notable ancestry companies.

These companies use maternal haplogroups as a resource to determine ancestry.

Many people using these tests do not realize how these tests actually work and the wrong information they present at times. The first issue resides in the health screenings of these ancestry tests. They claim to use your ancestry to see if you are at risk for Alzheimers, certain types of cancer, Parkinson’s, or what type of body type you have. These companies are not completely lying, however the tests can omit certain things and it is no substitute for going to an actual doctor.

Everything they search for is compared to a reference population, therefore your genes are merely compared to other people who are considered healthy or unhealthy. These tests do not have access to medical history in order to look for other clinical factors that could accelerate or further exacerbate this potential condition, thus explaining why it is irresponsible to tell people they are at risk for a debilitating disease because someone with similar genetics reported developing a disease that could have resulted from his or her specific lifestyle.

The issue with self-reporting in ancestry tests also can be seen in testing for heritage. The data these companies use are based off of reference populations (many of which are self-reported especially in the early years of the tests), therefore the same person can receive different results at different times. The database is constantly changing (which isn’t necessarily only a bad thing) so if the same person takes the test three times in three different years, they are likely to get different results. If the company recently expands to selling DNA kits in a new area of the world, a person with mixed heritage from the United States can receive different results because the test population of a certain region was extremely small and unspecific before, whereas now they have more of a test population that can change “how Vietnamese you are” (or whatever region that applies to you).

Have you ever known someone who took the DNA test and found out they were not as Greek or Russian (insert anything) as they thought they were? These results are problematic on so many levels when breaking down ancestry. The first example is that when comparing extremely similar populations, your heritage might not reflect your ancestry that the test finds. For example: modern English, Scottish, and Irish people have vastly similar results in these tests because they are very similar genetically and geographically, therefore a person can find out they are 50/50 Irish and English, however all of their known relatives can be traced back to 1870s Ireland. The person is not “less Irish than they thought”; it merely means that centuries of migration and conquering in the region of the British Isles could blend the gene pools even if this person’s family tree of the last two-hundred years can be traced back to one specific town.

Something else important to consider is that ancestry and heritage are not nearly synonymous terms. Furthermore, two twins could receive different genes from the same parents which could lead to slight changes in genetic makeup. Your sibling is not “more Swedish than you” in terms of heritage and the culture you were raised in. The sibling might receive a certain gene from your parents that you did not.

While there are a myriad of problems and hypotheticals to bring up, I will leave you with one last problem. Groups of people that live in diaspora such as Jews, Romani, and Armenians could have problems with these tests. Ashkenazi Jews from Eastern Europe live in diaspora and have been a migratory group for centuries, leading them to mix in with various gene pools that they settle in. When an Ashkenazi Jew or Romani (who similarly lived a migratory history) takes an ancestry test, they could feel completely related to their Ashkenazi or Romani heritage, however the intermixing of people over centuries (because they settled in so many places) could come up in the test even though they feel like they have no relationship to the heritage at all. Romani people also are difficult to pinpoint to one specific region of origin which demonstrates another potential problem with the tests.

While these tests can be a fun activity to do with your friends, make sure you take the results with a grain of salt because you are not necessarily “less French than you thought”.

BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: ancestry

Where Did Father’s Mitochondrial DNA Go?

The Problems with Ancestry Tests (23andMe, Ancestry.com, etc.)

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