Who are my ancestors?
That is a question that often spontaneously bursts into people’s mind. Sure, the majority of us know who our parents are. Some of us may even be fortunate enough to know/remember our grandparents. But great-grandparents? Great-great-grandparents? Even for those that have kept a detailed family tree, it still comes to an end eventually. What many people don’t realize is that within us, we all contain the key to our origin and that key is our DNA.
In short, DNA, or to use its full impressive name deoxyribonucleic acid, is the genetic material that governs all the functions of your body. Viewers of popular crime series such as Law & Order or CSI may know DNA as a piece of evidence that can prove whether or not a potential suspect was at the scene of a crime. After all, a person’s unique DNA is present in the nucleus of every single cell of a human body, anything that the criminal left at the scene of a crime such as a piece of hair or blood can be used to decode the criminal’s DNA. However, to trace back a person’s ancestry, it is not the nucleus’ DNA that scientists are interested in but the DNA within the mitochondria.
Mitochondria, the organelles within each cell that produces energy for the body to function, also contains their own DNA. What’s unique about the mitochondrial DNA is that it came strictly from your mother. Why? Because the mitochondria within the sperm had the task of providing enough energy for the sperm to swim up the uterus and fertilize the egg. After the successful fertilization, the tail of the sperm (along with all your father’s mitochondria) falls off and so the fertilized egg only contains your father’s nuclear DNA. Since your mitochondrial DNA must be identical to your mother’s (and naturally, your grandmother’s, great-grandmother’s and so forth). Any differences within the mitochondrial DNA would have occurred due to spontaneous mutation. Since mutations within the mitochondrial DNA doesn’t occur fast enough that it is too hard to trace back the mutations yet it occurs not slow enough that everybody’s mitochondrial DNA is identical, scientists are able to trace, through the mitochondrial DNA, their ancestry.
For example, it was always speculated that all the pet golden hamsters in the world are the descendants of just one female hamster but for decades, there was no concrete fact that supported this statement. However, through the collection of mitochondrial DNA of pet hamsters from all around the world, it was discovered that they were all 100% identical. So it was true, all the pet golden hamsters in the world are descendants of just one female hamster, which is an amazing thought.
Building upon the previous example, scientists have managed to trace back everybody’s mitochondrial DNA to one of just seven women (This is in Europe). In his book “the Seven Daughters of Eve”, Bryan Sykes talks about his research and the steps he took over the years to come to this amazing conclusion. Naturally, since males cannot pass on their mitochondrial DNA, there may be more women (“Eves”) whose mitochondrial DNA didn’t get passed on because they only gave birth to sons.
So how can you trace back your paternal line? I hear you ask.
Well, just like all the mitochondria within your body came solely from your mother, there is also genetic material within your body that would have came solely from your father. The chromosomes that determine the gender of any child are called the X and Y chromosomes. Females have XX chromosomes while males have XY chromosomes. Since both sex chromosomes of a woman is X, for a child to be a boy, the Y chromosome must have come from his father. So within males, their paternal line can be traced back via the Y chromosome. Naturally, as in the case with males and mitochondrial DNA, since females do not have any Y chromosomes, their father’s paternal line stops at them.
So there you have it, a brief overview of how we can all trace back our ancestry through our DNA. And as Bryan Sykes adequately said at the end of his book, DNA is “not ‘just a chemical’ after all, but the most precious of gifts”.
Recommended reading: “The Seven Daughters of Eve” by Bryan Sykes
