The body is composed of cells. Below are a couple of kinds of cells found in the human body; blood cells, cheek cells, muscle cells, and skin cells. Every cell in the body except a red blood cell has a large dark spot called a nucleus, which contains its genetic instructions that tell the cell how to grow and how to function, and that makes it possible for the cell to divide and make more cells.
In each cell is a nucleus, and the nucleus contains genetic material that tells the cell how to develop and what to do. There are also other structures inside cells that carry out vital functions.
Each piece of genetic material is a gene, and the genes are organized into chromosomes. Everyone has two sets of chromosomes, one from each parent.
Each person has a pair of every chromosome, except for the pair of chromosomes that tell the body whether to be a man or a woman. These chromosomes are two X chromosomes for a woman, and an X and a Y chromosome for a man. A girl got one X chromosome from each of her parents. A boy got an X chromosome from his mother, and a Y chromosome from his father. The fact that a boy necessarily got his Y chromosome from his father is very important for genetic genealogy.
Chromosomes contain genes. Genes are sections of genetic code that tell the cells of the body how to develop and what to do. Genetic code consists of four chemical units, coded by four letters. The DNA is organized in two strands, that are bound together, and form a spiral.
Whenever there are two chromosomes with pairs of genes, the genes can recombine. This means that oneís chromosomes never exactly resemble any of oneís parentsí four chromosomes. The genes, and even sections of code within genes, have moved around between the chromosomes. This makes it impossible to look at someoneís genetic code on these chromosomes, and know which long ago ancestor it came from.
However, a man has only one Y chromosome, and his sons got his entire Y chromosome. This means that the genetic code on the Y chromosome cannot recombine. This is very important for genealogical and anthropological genetic research. A manís Y chromosome looks exactly like that of his father, and that of his father, and so on, except for very small changes that may have occurred between generations.
Usually a sonís Y chromosome looks exactly like his fatherís, but sometimes there are small changes. Such small changes in genetic code between one generation and the next are called mutations. There are several sorts of mutations, and they have different uses Some changes, called short tandem repeats, or STRís, make it possible to tell if two men may be related, or if two families share one male line ancestor.
Other mutations, called single nucleotide polymorphisms, or SNPís, make it possible to tell how groups of people moved around through time. They also make it possible to tell how oneís own direct male line ancestors moved around through long periods of time.
For instance, Theophilus McKinstryís direct male line ancestors have lived in Scotland for about 1700 years, and came from England, where they probably lived atleast since 2000 BCE. Before that they lived in or near the German Rhineland, They spent the last ice age in east central Europe, north of the Balkan mountains, and reached northwestern Europe when the ice age was over, by pursuing herds of deer. In east central Europe during the ice age, they belonged to the most advanced culture of their time and transformed the way people lived. We pretty much know all of that for a fact.