National Grigsby
Preservation Foundation

Genetic Genealogy:
The New Science of Discovery of Human Family History

By Donald Linn Grigsby, Ph.D.

How do we really KNOW that we descend from an ancestor who live many generations ago?

That question was recently asked by the son of one of our National Grigsby Family Society members.

The answer to that question is not as simple as one might initially believe; and before April of 2003, the date of the completion of the worldwide Human Genome Project, there WAS in reality NO WAY to PROVE that we were descendants of an ancestor many generations ago. All that we had to rely upon prior to 2003 were family oral traditions and paper records, some of which proved to be incorrect. Today, however, we can learn the story of our ancestry from a record that is indisputable, and we now understand how to read its language code, and we understand the process by which it is passed from generation to generation.

Since individuals of a widely varied age and knowledge background will doubtlessly ask the same question, I will attempt to provide an answer that may be redundant to some, but satisfactory for the youngest and least knowledgeable.

Every male has both sex chromosomes X and Y along with 22 pair of autosomal chromosomes making 23 pair total. Females have two X sex chromosomes as one pair along with 22 pair of autosomal chromosomes making 23 pair total.

During the production process of ova for the female and sperm for the male, the paired chromosomes separate with one half of each pair being included in each ovum and each sperm cell. When sperm and ovum unite to form a zygote cell, the zygote cell has once again 23 pair of chromosomes. Each ovum has one or the other of the female’s X chromosome pair, while the sperm with which it unites may contain either an X chromosome or a Y chromosome. When two X chromosomes unite, the child will be a female. When an X and a Y chromosome unite to make a pair, the child will be a male. The DNA instructions on the Y chromosome will be to produce identically itself to be passed on to each new generation of males. So, Immigrant John Grigsby passed his identical Y chromosome on to each of his sons, and they to their sons, and on and on, generation after generation in an unbroken chain.

Each Y chromosome is made up of millions of nucleotides. There are four kinds of nucleotides (adenine, cytosine, guanine, and thymine, indicative of the acid base of the nucleotide. Think of them as a four-letter alphabet upon which the instructions are encoded to create an individual and maintain its function throughout its life).

Just as on a product assembly line, occasionally a defective item is produced. Although the body has an extremely effective system which eliminates the rarely created defective products, on very, very rare occasion, a defect gets by. If that mutated nucleotide is on the Y chromosome and results in the creation of a son, that son will have a Y chromosome like his father’s and brother’s Y chromosome’s millions of nucleotides – with the EXCEPTION of ONE nucleotide on ONE gene which we label a Single Nucleotide Polymorphism (SNP). That SNP for that individual will be replicated by that individual (it is all he has to replicate) and passed on to each of his sons, and they too to their sons, generation after generation, until another SNP may occur again changing one nucleotide of the millions of nucleotides passed to ONE son who then passes it to ALL of his sons, etc., etc.

A Y chromosome nucleotide mutation (SNP) which result in a birth of a son occurs roughly, on average, about once every 150 years in each of the four Grigsby lines from the John Grigsby (1623-1730). Some variance exists between surname families and among surname family lines.

An actual example should clarify the situation.

The “Immigrant John” Grigsby (1623-1730) had five sons who had received his Y chromosome and a daughter who had received his X chromosome. We can look at the 40-plus current-day male descendants of John Grigsby and the Y-DNA he has passed down that is shared by ALL of his patrilineal descendants (this excludes the SNPs which have occurred later and are exhibited by some but not all of his patrilineal descendants) and we discover what “Immigrant John” Grigsby’s Y-DNA exhibited that he inherited from his father.

The Y-DNA that “Immigrant John” passed to sons John, Charles, and William was identical to his own (exact copies with no defects/changes). The Y chromosome that he passed to James, however, was different from that inherited by his brothers.

On one of the genes, one nucleic acid base on one nucleotide had switched from thymine inherited by his brothers, to cytosine (T to C), which we discovered and named the SNP JFS0016. All of the sons and later patrilineal descendants of the Immigrant John Grigsby son James Grigsby will exhibit the SNP JFS016 nucleotide, which has cytosine as an acid base, while all other Immigrant John patrilineal descendants will exhibit thymine as an acid base at that same location. This one SNP “marker,” therefore, allows us to easily identify any patrilineal descendant of the James Grigsby (I) line.

In the line of the “Immigrant John” son Charles Grigsby, Charles passed a mutated Y chromosome to his son “Soldier John” Grigsby. While the other sons received an identical Y chromosome that Charles himself exhibited, “Soldier John” Grigsby received a chromosome with a defect/change in one of the millions of nucleotides. On the chromosome inherited by “Soldier John” was received the SNP JFS0014, which had one nucleotide that had switched from thymine to cytosine. So, while his father, brothers, and all of his Grigsby male cousins exhibit thymine at the SNP JFS0014 position, “Soldier John” and all of his patrilineal descendants exhibit the acid base cytosine at that location on the Y chromosome.

In my line, the third generation Benjamin Grigsby (I) received a mutation in one nucleotide at the SNP location JFS0012 when the acid base adenine had switched to guanine. So, while his father and brothers and all of his Grigsby male cousins exhibit the nucleotide adenine at the location we have named JFS0012, all of us who descend from the John Grigsby (II) son Benjamin Grigsby exhibit the nucleotide guanine at that SNP location named the JFS0012.

For those of you who have long since fallen asleep, I extend my sincere apologies. For those of you who are still awake, this is how I inherited “Immigrant John” Grigsby’s Y chromosome DNA passed down from father to son for 10 generations, with the change of a couple of nucleotides out of the 37,000 nucleotides we tested from my Y-DNA sample. All the other Y-DNA nucleotides that make up my Y chromosome were produced in exact replica and faithfully handed down male generation after male generation from “Immigrant John” to me.

It should be understood that in addition to Y-DNA, which is passed down essentially unchanged from generation to generation, approximately half of the other 22 autosomal chromosomes are also passed from each parent to each child. It is reduced 50% with each new generation, allowing a place for the autosomal DNA of the spouse’s side of the family.

The point being made that descent from “Immigrant John” can be through DNA other than Y-DNA analysis of autosomal DNA is, however, above my pay grade. Anyway, something needs to be left to frustrate others.

Other SNP markers that we have discovered and analyzed designate branching at various generational points in the Grigsby family tree.

We determined, early on, to abandon the STR research path being followed by other surname family researchers, and to formulate our own analytical approach based upon SNPs instead. It has provided outstanding results.

Donald Linn Grigsby, Ph.D., NGFP Board of Directors, Y-DNA Study Committee Chair