DNA Testing: What is it and where can I get it done?

A few correspondents have asked about what kind of DNA testing is available.  There are four basic types of DNA testing for genealogical purposes:

1. Y-Line DNA
2. Mitochondrial DNA
3. Autosomal DNA
4. The X-Chromosome

The four basic kinds of DNA testing are described well at the DNAeXplained blog.  I'll summarize below:

1. Y-line DNA – tests the Y chromosome which is passed from father to son, along, in most cases, with the surname.  Only men can test for this, because only men have a Y chromosome.  We compare the results of the Y chromosome test between males to see if they match and are related in a genealogical timeframe.  We also obtain the haplogroup which defines deep ancestry, such as European, African, Asian or Native American.  Surname, haplogroup and other interest projects (such as Cajun, Melungeon, etc.) exist for both Y-line and mitochondrial DNA at Family Tree DNA.  These projects are indispensable for both genealogy and genetic genealogy research.
2. Mitochondrial DNA – is passed from mothers to both genders of her children, but only passed on to descendants by females.  Males carry their mother’s mitochondrial DNA (mtDNA) but they don’t pass it on.  We compare mutations to see if people share an ancestor in a genealogical timeframe, but because the surname changes in every generation, it’s more difficult genealogically to make the connections.  Mitochondrial DNA testing also provides a haplogroup which defines deep ancestry, such as European, African, Asian or Native American.  Family Tree DNA is the only commercial company to offer full sequence testing which is sometimes necessary to determine whether a match is really genealogically relevant. 
3. Autosomal DNA – tests the rest of the DNA provided by both parents on the 23 chromosomes, not just two direct lines, as with Y-line and mitochondrial DNA.  Older tests of this type tested between 21 and about 300 markers, but current generation testing provided by Family Tree DNA (Family Finder test), 23andMe and AncestryDNA test use about 700,000 locations and are in an entirely different category in terms of their usefulness and accuracy to genealogists.  These tests provide a list of cousins from all of your lines, but it’s up to you to figure out how these cousins are related to you.  The testing companies provide different tools to help in this quest.  Both Family Tree DNA and 23andMe provide the ability to download your raw data results so that you can do further analysis personally and by using several online tools, the most popular being GedMatch.  AncestryDNA, the autosomal test through Ancestry.com, does NOT provide this capability and is deficient in other matching tools, providing no chromosome mapping or comparison capabilities, leaving customers significantly in the dark as compared to the tools at Family Tree DNA and 23andMe.  Autosomal tests also provide an estimate of percentages of ethnicity. 
4. The X Chromosome – has special inheritance properties that allow people to use these results separately from the rest of the autosomal results, although the X chromosome is a part of the 23 sets of chromosomes used for autosomal testing.  The inheritance paths are different for males and females, because males only inherit an X chromosome from their mother (and a Y from their father which makes them male), but women inherit an X from both of their parents.  At this point, both Family Tree DNA (FTDNA) and 23andMe include X raw data in their downloads.  Ancestry does not include any X matching or data, so you cannot use the X chromosome information in any way if you have tested at Ancestry.

You can test at 23andMe, Ancestry or FTDNA for autosomal DNA and get basically the same results.  Each service has its advantages...23andMe has scale, since they have tested hundreds of thousands of persons, however, most are interested in the medical results not the genealogy.  Ancestry and FTDNA have a genealogy-focused customer base but are significantly smaller than 23andMe.  However, don't worry, you can upload your results to GEDmatch where customers of any testing service can match on each other's results.  I encourage all Skaggs descendants to upload their autosomal DNA results to GEDmatch.

For Y-Line and mitochondrial DNA testing FTDNA is the place to go.  There is a Skaggs project there that you can join.