Last December, I bought a DNA kit from Ancestry.com, the online subscription site for genealogic records. As a subscriber, I was able to purchase the kit for a reduced price of about $100.

A week after making the purchase on line, I got the kit. I had to partially fill a small tube with about 5 cc of my saliva and return it.

In late January came an email from Ancestry.com, saying that my test had failed because I hadn’t submitted enough saliva. I was sent another kit, put twice as much sputum in it, and sent it back.

In two weeks, I got another form email, saying the same as the other: my test had failed and they were sending me another kit!

I asked around with others who had had, or had heard of, similar experiences, and it was suggested that the next time, I chew a little on my inner cheeks before filling the tube. I did so for the third kit, submitted it, and last week got another email from Ancestry.com, saying their analysis would take six to eight weeks.

I had hoped that by now, I could give some personal comments on DNA testing, but that will have to wait until I receive results. I’ve heard that such “rejection” is not uncommon with any of the venues that offer DNA testing.

I previously spoke of the DNA in the chromosomes of the cells of all human beings: 22 paired autosomes (shared from mother and father), which essentially contain a complete genetic record, with all branches of a person’s ancestry at some point contributing a piece of his or her autosomal or shared DNA (auDNA).

I also mentioned the 23rd pair, the sex chromosome pair, which, in women, has two X chromosomes: one from the father, one from the mother. In men, the 23rd chromosome has only one X from the mother, and from the father, a Y chromosome that contains paternal or Y-DNA.

In addition to the DNA in chromosomes, a special type of DNA exists called mitochondrial DNA, maternal DNA, or simply mtDNA. It is handed down only from females. A male receives mtDNA from his mother but passes none to his children. mtDNA mutates very slowly (approximately every 50 generations), so it is valuable in genealogic analyses.

A chromosome is a single piece of coiled DNA, while mtDNA has a circular shape. Both contain the material that controls the inheritance of eye color, hair color, and many other human characteristics. The contents and arrangement of these elements define any human as an individual, and the similarity of certain elements can be used to determine how closely two different donors of DNA are related.

A grasp of these concepts is necessary in order to understand how DNA testing can provide genealogic information. The testing can be done on shared DNA (auDNA), on paternal DNA (Y-DNA), or on maternal DNA (mtDNA). The type of DNA that is used determines which genealogic information may be found, and to an extent, how reliable the results may be.