There are currently three types of DNA that are generally used for genealogical research.
The first type is Mitochondrial DNA (mtDNA) which is found outside the nucleus of the cell. This type of DNA is found in the human egg but not in sperm so it is passed down almost unchanged from a mother to her children, allowing you to trace your maternal ancestry. Males have their mothers mtDNA but do not pass it on to their children. National Geographic identified my mtDNA haplogroup (more on haplogroups under Y-DNA) as U5B2A1B which is associated with NW Europe (UK, Germany, Ireland and Scandinavia). Since the focus of this Web Site is on the Newell family, I won’t dwell on the results from my mitochondrial DNA test, which relate to my mothers side, but there is one interesting story regarding a distant relative; Cheddar Man, a Mesolithic individual from prehistoric Britain dating to 9,150 years before the present, was determined to have belonged to Haplogroup U5 the parent group of my mt-DNA sub-group.
The other types of DNA used in genealogy research are contained in the cell nucleus and is packaged in 23 pairs of chromosomes. For DNA based genealogical research this nucleic DNA is divided into autosomal and Y-DNA depending on which chromosomes it is packaged in. The first 22 chromosome pairs are the autosomal chromosomes. In these, each member of the pair has the same structure: however, in the 23rd pair (the sex chromosomes) the structure differs depending on your sex. If you are female you have a pair of X chromosomes; however, if you are male you have a X and a Y. The Y is smaller than the X so the two members of the pair differ. Whether you are male or female is determined by your fathers sperm which can contain either X or Y. If a sperm containing a X fertilizes the egg then you become female (XX) but if a sperm containing a Y fertilizes the egg then you become male (XY). DNA from the Y member of the 23rd pair of chromosomes in males is the other type of nucleic DNA commonly used in genealogical research. This Y-DNA (only found in Males) comes from your father and was passed down from his father like the family name in European cultures. Females do not have Y DNA so they cannot do this test. When genealogist first started using DNA they initially focused on Y-DNA since it was ideal for tracking the European family names (male ancestors).
Recent developments in the analysis of autosomal DNA and the development of large autosomal DNA databases by organizations like Ancestry DNA have resulted in autosomal DNA becoming the most common type of DNA used for genealogical research. Y-DNA and mt-DNA are still used especially for tracking longer term (> 6 generations) family roots. There is a in-depth review of my Y-DNA results in a separate section on Tracking the deep roots of my early Newell ancestors.
The Autosomal DNA which is inherited from the autosomal chromosomes (chromosomes 1-22) contain most of the DNA which determine how we look and function (the main exception is which sex we are, which is determined by the 23rd pair). In humans and most other complex organisms, one copy of each autosomal chromosome is inherited from the female parent and the other from the male parent. This explains why children inherit some of their traits from their mother and others from their father. Basically you randomly get half of your autosomal DNA from each parent who got half from each of theirs so you got approximately 1/4 of your DNA from each grandparent and 1/8 from each great grandparent. Test of autosomal DNA gives us a measure of the DNA we inherited from all of our ancestors but since DNA gets diluted in each generation it is less useful in identifying DNA matches beyond 4th cousins (common GGG Grandparent) since the amount of DNA you each receive from each GGG Grandparent is so small. Due to the relatively small percent of common DNA and random variations in the way DNA gets passed on it is likely that you might not get a DNA match to some of you 4th cousins. Here is what Ancestry DNA says about matching 4th cousins (common GGG Grandparent): Our analysis of your DNA predicts that the person you match with is probably your fourth cousin. The exact relationship however could vary. It could be a third cousin once removed, or perhaps a fifth or sixth cousin. For relationships this distant from you, there is greater statistical variation in our prediction. It’s most likely to be a fourth cousin type of relationship (which are separated by ten degrees or ten people), but the relationship could range from six to twelve degrees of separation. It’s interesting to note that (at this degree of separation) we are accurately able to predict only about 71% of the possible relatives that are out there—in other words there is a 29% chance that our DNA analysis can NOT recognize an actual relative of yours. One way to be more certain that the DNA testing captures as many relatives as possible is to have multiple members of your immediate family tested. The actual percent and location of DNA inherited from each parent can vary and so there are methods, e.g. common segments and centimorgans, that can be used to measure DNA connections (see: https://isogg.org/wiki/Autosomal_DNA_statistics ). Even though the DNA you share with distant cousins (5th and greater) is relatively small it is still possble to find matches at the 5th cousin level and beyond. The possibility of finding distant matches increases in cases where your ancestors were from areas where there was a small group of original settlers (founder effect) with subsequent limited in migration. In these cases a process called Endogamy can increase the probability of finding distant DNA matches.