The 23rd pair of chromosomes is comprised of sex chromosomes – X and Y chromosomes that determine whether you’re male (XY) or female (XX). Traits like red-green color blindness, male pattern baldness and hemophilia are specifically linked to X or Y chromosomes and are called sex-linked characteristics. All of those examples, and most other sex-linked traits, are X-linked and more common in males, who only have one X chromosome. Many DNA tests isolate Y DNA in males to show consumers their paternal haplogroup. Since the Y chromosome is directly inherited from father to son, it is possible to trace direct paternal lineage for many generations.
In fairness to 23andME, it leaves it up to the customer to unlock the more serious results – or not. When I unlock mine, I discover that, while I’m not genetically predisposed to such things as the BRAC1 or BRAC2 variant, Parkinson’s or MS, I have one of the variants for late-onset (mid-80s) Alzheimer’s. However, I don’t have any other markers for Alzheimer’s or family history or conditions associated with it or anything else listed in the rather lengthy disclaimer, which also stresses that it’s not a diagnostic result and to seek further advice from your GP if you are concerned.
Whether it’s an autosomal test, a Y-DNA test or an mtDNA test, virtually all providers use the same science. Some providers offer an ‘off the peg’ solution such as Ancestral Origins™ or AncestrybyDNA™, so if you’re interested in these you should shop around for the lowest price. Most providers offer a test that interprets and presents the results in a unique way, so if one of these catches your eye, look for examples of how the results are presented on their website before you buy.