DNA and Father's Day
June 10, 2020
In Bill Bryson’s 2003 book, A Short History of Nearly Everything, he writes, “If your two parents had not bonded when they did—possibly to the second—you wouldn’t be here.” Your existence also depends upon countless exact bondings between your grandparents, great-grandparents, all of your forefathers back thousands of years.
Bryson has counted up all the people required to make you, You. He says that “if you count back sixty-four generations, to the time of the ancient Romans, the number of people on whose cooperative efforts your existence depends has risen to a giant number, a 1 followed by eighteen zeros, which is several thousand times the total number of people who have ever lived.”
Bryson then writes, “Clearly something has gone wrong with our math here.”
He explains this riddle by allowing for some incest in most people’s genealogy, “actually quite a lot of incest—albeit at a genetically discreet remove.” If a typical father and a mother would trace their genealogy back far enough, it is most probable that they would discover a common ancestor.
Bryson writes, “In the most literal and fundamental sense, we are all family.”
In 1953, two scientists, James Watson and Francis Crick, were working at the Cavendish Laboratory in England, when they struck upon a model for DNA, deoxyribonucleic acid, Mother Nature’s means of transmitting genetic information from one generation to the next.
DNA, Watson and Crick hypothesized, is “rather like a spiral staircase or twisted rope ladder: the famous double helix.” Stretched between the two side strands are a series of steps or rungs composed of two of four possible nucleotides: adenine, thymine, guanine, and cytosine.
This DNA is found in two places within a cell: in the chromosomes inside a cell’s nucleus, and also inside the mitochondria, the cell’s “power house” that produces its energy.
First, y-Chromosomal DNA inside the nucleus.
Human beings have 22 pairs of chromosomes, plus another pair, the 23rd, that determines a person’s sex. Two X chromosomes produce a female, but an X matched to a Y produces a male.
A son receives his Y chromosome from his father, who received it from his father, and so on back through the generations. It is patrilineal, passed through each generations’ fathers.
Today, geneticists have identified certain mutations within men’s y-chromosome, and from those slight differences, they categorize men into 17 different y-chromosomal families, called haplogroups.
All members of a certain haplogroup share the same y-chromosome mutations. The Haplogroups include: A, B, D, E, C, G, H, I, J, L, T, N, O, S, M, Q, and R. Because my paternal great-grandfather, Bernt Berntsen, was Norwegian, most likely I reside within the Haplogroup I, or possibly R1a or R1b.
A genetic study would quickly determine which it is. Perhaps someday.
Geneticists have labeled that first father without any of the current identifiable mutations in the genetic code, Y-Chromosomal Adam, the most recent common ancestor, MRCA, of all living humans.
Not that there were no other men living when this Adam lived, but their genetic code did not pass down to the men of today, as did this anonymous Adam’s DNA.
Now, mitochondrial DNA. A child receives his or her mitochondrial DNA from the mother, who inherited it from her mother, and so on back through the generations. It is matrilineal, passed through each generations’ mothers.
Geneticists have also identified certain mutations on the mitochondrial DNA, and from these, they have built groups or categories of women, based upon those identifiable mutation markers.
Geneticists call that first woman of a prior generation without any identifiable mutations in the genetic code, Mitochondrial Eve, the most recent common ancestor, MRCA, of all human beings.
All agree that both this Adam and this Eve lived in East Africa thousands of years ago, but they debate over when the two lived, and who lived first, either y-Chromosomal Adam, or Mitochondrial Eve. The estimates are over 500,000 years ago to about 58,000 years ago.
Bryson writes, “We are alike. Compare your genes with any other human being’s, and on average they will be about 99.9 percent the same. The tiny differences in that remaining 0.1 percent are what endow us with our individuality. DNA has been called, ‘the most extraordinary molecule on Earth.’”
All children look to their mothers for their mitochondrial DNA, but boys and men look to their fathers for their y-chromosomal DNA. It is science and it is biology, difficult to understand, but it is the substance of our beings, that work completed at the cellular level, of which we are unaware.
Fathers’ Day approaches.