|Tell me more about Y-DNA testing|
|Y-DNA testing is a tool that can be used to assist those interested in genealogy to trace their family tree. It is best used when coupled with genealogy done the old fashion way. To better understand Y-DNA testing, one must first reflect on some basic biology principles.
Every cell of the human body contains 46 chromosomes or 23 pairs of homologous chromosomes (similar chromosomes). These chromosomes carry the genetic code for why we look the way we do. This genetic code is found in the sequence of nucleotide bases that make up the DNA. We each inherited 23 chromosomes from each parent to make our 23 pairs (46 chromosomes).
When cells divide to make new cells, the chromosomes are copied so that each new cell gets 46 chromosomes. This process of cell division is called mitosis.
Some cells of our body are specialized in making gametes or sex cells (egg and sperm). When these sex cells are produced, the number of chromosomes is reduced in half. Each sex cell gets 23 chromosomes instead of 46. The 23 pairs of homologous chromosomes pair up and then seperate during a process called meiosis. After the pairs seperate, the cell divides creating two new cells each with only 23 chromosomes. Which cell gets what chromosome is a 50-50 chance. It is completely random. In essence you wind up with DNA from all of your predecessors throughout history.
There is one pair of chromosomes that is of particular interest to the genealogist. These are the sex chromosomes. Females have two sex chromosomes (X,X) and males have (X,Y). In the case of females, one of their X's came from her mother and one of her X's came from her father. In the case of males, his X came from his mother and his Y came from his father. The Y is only carried by males and is passed from father to son , from his father, from his father, etc.
The Y chromosome (Y-DNA) has been passed from generation to generation unchanged for hundreds of years. Males who have descended from a common male ancestor should in theory have identical Y chromosomes (Y-DNA). By comparing Y-DNA, one can tell if two male individuals share a common male ancestor.
Unfortunately for females, this is not possible. If one studies her X chromosomes, one cannot trace the origins of the X chromosome. Sure she would have received on from each of her parents, but her mother's X could have come from her mother's mother or father. The X she received from her father would have come from his mother - which could have come from her mother or father. This randomness does not assist the genealogist in tracing back a surname or lineage which in many western societies is based on surname of the males.
It is purely coincedental that the inheritance of the Y-chromosome happens to follow this pattern of surname inheritance. About 900 years ago when surnames were first used, they had no idea about DNA, sex chromosomes, or even sex cells. There was a period of time, just a couple/few hundred years ago, when they thought that a human embryo was contained within the tiny sperm cells and simply transferred to the female in order to develop.
Back to a statement made earlier..."In theory the Y-DNA has not changed for generations"...In many, if not all, family lines there have been situations where male children were adopted into families and given the surname of the adoptive father. In this case the adopted child would still have the Y-DNA of his biological father which would be different from the Y-DNA of the adoptive father. There have also been many situations when a female would pass her surname onto her child and not use the surname of the biological father. This child would then have Y-DNA that is different than the surname lineage. Folks, these situations have occurred in all family lines at some point in the last 30 generations (900 years) or so that surnames have existed. Each surname will very, very likely have a few or more different Y-DNA lineages established. This is to be expected. Still, knowing all this helps to deterimine relationships of individuals descending from a known common male ancestor.
For example, in my own surname Haupt, I know of a few different Y-DNA lineages (there are likely others). My surname can now be found throughout Europe (and around the world - often with spelling derivations). While the name originated in Germany during the very early 1100's, there were branches from this line established in France, Austria, Switzerland, Poland, Czech Republic, Romania, Russia, Hungary, etc. during the 1300's-1500's. A individual today living in the United States sharing the same surname can, using Y-DNA testing, can come closer in determining the origins of his Y-DNA lineage. A Haupt in the Czech Republic has Y-DNA different from my own. There will even be different Y-DNA lineages for the same surname within the country of origin - in this case Germany.
It was also stated earlier that Y-DNA is passed from father to son unchanged over many generations. Well this is mostly true. In the course of 30,000 years, there have been occasional mutations that have occured to the Y-DNA code. These rare changes produce the different haplogroups. A haplogroup is a population of individuals with fairly similar Y-DNA test results. For example, 45-50% of males in Southern Germany will be in the R1b haplogroup which indicates that this population as a whole shared a common ancestor further back in time. By knowing ones haplogroup, one can better understand the path or route the most distant ancestors travelled before populating this region.
What do the numbers on the test results show?
The Y-DNA test results are reported as a listing of DYS codes (markers) and a number beside each code (marker value). The markers are specific locations on the Y-chromosome where the nucleotide sequence is studied. The backbone of each nucleotide is its nitrogen base. There are four types of nitrogen bases making up DNA. These are Adenine (A), Guanine (G), Cytocine (C), and Thymine (T). These four nitrogen bases sequence themselves in units of four nitrogen bases; Here is an example:
AGTC GCAT CCCA TCTA GGCC ATAT GTGC TTAG AGGC TCCC
At the marker locations on the Y-DNA chromosome, it was discovered that these codes repeat themselves. A sequence of repetitive four nitrogen base codes can be thought of as a gene. Here is an example:
AGTC TCAA GGCG TCTA TCTA TCTA TCTA TCTA TCTA TCGC
In the above example, at this particular marker, the marker value would be 6 since the TCTA repeated itself 6 times. At this same marker location, another non-related individual would have a different marker value. Closely related individuals (same lineage) would have the same marker values for each of the marker locations.
The Y-DNA chromosome is 10's of thousands of nucleotides long. Lab techniques, equipment, etc. are all used along with computers to produce the nucleotide sequence either on screen or as a printout. The marker locations are determined and then the marker values are then determined.
You have your choice in whether you want 12 markers studied, 37 markers studied, or 64 markers. Each provides additional level of detail. Based on the accumulated marker values, a prediction can be made as to what Haplogroup these results fit in. A futher test is needed to conclusively show the exact Haplogroup. This is often called a backbone test. The backbone test determines the presence of specific Y-DNA mutations that have occured in your distant past. The presence or absence of these specific mutations will determine the haplogroup.
After you have the results, you will want to compare your results with others. You are encouraged to join surname project groups, or other Y-DNA databases. Two rather large Y-DNA databases are Y-Search and Y-Base.
What is mtDNA?
This is mitochondrial DNA. It is a specialized DNA found in the mitochondria of each cell in your body. The mitochondria are the "power house" organelles found in the cells. The mtDNA is contained in the mitochondria of the egg cell. Therefore, all mtDNA comes from the mother. The mother passes her mtDNA to both sons and daughters. The sons however do not pass their mtDNA on to their offspring - only the daughters can. By having a mtDNA test done one can learn of the female lineage (mother, grandmother, great-grandmother, etc.) back in time. It will not help you to trace a surname or show relationships based on surname.
Ray Haupt (Aug. 2009)
BA Biology (UNC-G 1979)
Former Biology Educator