A full restructuring of the DNA pages is pending, but initial steps are underway. Apologies for any oversights.
DNA testing can provide evidence to be used alongside traditional genealogical evidence (“paper trails” and so on). Like all types of evidence, it should be interpreted with care, but testing can provide evidence even if no other documentation remains, so it should be considered in any genealogical searches to see if it might be applicable. And while “ethnicity” estimates are one aspect that is marketed to the public, that is not the main genealogical utility of these sorts of tests.
Generally speaking, genealogical DNA testing is decidedly a “group sport”; one person’s results, in isolation, have nearly no utility at all, as it is comparison/matching of results that give them meaning and utility. Fortunately, the last 20 years has seen genealogical DNA testing go from a rare and very expensive tool (early testers often paid well over $1000 for testing!), to a much more affordable and increasingly common thing. Now, in addition to the ability to test 2 or more people to see if they are related (pretty much all one could do in the early days, since almost nobody had tested), one tester can often find new “matches,” who represent cousins of various distances. Those matches are used in attempts to identify the common ancestors, or at least which branch of your ancestors are where the ancestor should be found, and thereby gain new leads for future traditional genealogical research. Thus, testers hope to be able to break down their genealogical “brick walls,” now or in the future.
There are three general “types” of DNA that can be tested, “autosomal DNA” (typically the cell’s nuclear chromosomes, excluding the Y-DNA), Y-DNA (carried only by males, passed on essentially unchanged from father to son, across the generations), and mtDNA (mitochondrial DNA, which exists outside the cell’s nucleus, and is passed down essentially unchanged, but only from mothers, to all her children). The Y-DNA is really the only one useful for researching a very old surname like Crawford, due to the characteristics and inheritance pattern of each one.
“Autosomal DNA” (used in tests from almost all testing companies, including Ancestry, 23andMe and MyHeritage) is a very useful genealogical tool for researching almost any of your ancestor lines (not just your surname line), since it is inherited, in part, from both parents, and thus, theoretically from all ancestors. However, it is not inherited equally from all grandparents, and since each child gets a random 50% of each parent’s DNA, this means the DNA of each ancestor is slowly diluted out until none at all might remain in you from a particular great great great (etc.) grandparent. This means it is quite good for identifying the precise relationships you might have to a given CLOSE match, by the time you get to a 4th cousin level, you have a chance of not matching your true cousin at all!
For the question of which older Crawford line (say, from the 1500s) you might descend from, autosomal DNA testing isn’t much help at all!! [It is worth noting that FTDNA is in late 2023 just starting to roll out a new feature of their autosomal “Family Finder test… They will soon give a basic Y-DNA haplogroup with it! I am hopeful this will become increasingly useful in seeing where those without dedicated Y-DNA testing can be assigned to the Y-DNA lineages, but time will tell how it goes]
Y-DNA (generally not included in any useful way by any of the main testing companies other than Family Tree DNA, aka FTDNA), in particular, is very well-suited to researching patrilineal surnames (surnames passed from the father), as both will transfer in an unbroken chain among all male-line descendants (barring surprises or unusual surname inheritance patterns). And there is no dilution in inherited Y-DNA like there is in autosomal DNA, which is a key factor making it the only useful genetic tool for researching older surnames like Crawford, which originated as a place name about 900 years ago!!!
Mitochondrial DNA (mtDNA) is found in all our cells, but is only inherited from the mother. It can be a useful tool for answering specific questions about one’s matrilineal ancestors (mother-of-mother-of-mother, etc.), but it cannot help with questions about one’s direct patrilineal ancestors (father-of-father-of-father, etc.).
Please visit the sub-pages under the Genealogy>DNA menu for details about the Y-DNA Project, and details about DNA testing!