Nuclear DNA of the cell is segregated into (a) the first 22 chromosomes, simply labeled 1 to 22, and termed Autosomes and (b) the Allosome or sex chromosomes, labeled X and Y. For Genetic Genealogy, Autosomes can be handled in bulk as we are not looking for particular genes that may exist on a specific chromosome but simply values across this whole collection of DNA. Most testing companies simply sample all the Autosomes and report the results back in bulk. Tools look at the matching of the sampled values and report percentage shared or matched when comparing two testers. They do this by looking for sequences of the same or very similar SNP values and using that to define a shared segment. SNP's exist at a particular location on a particular chromosome. Just the analysis results are reported in bulk and treated as such until looking for specific, matching segments of DNA in specific chromosomes.
The term atDNA is synonymous with the term Autosome. Because the Allosome xDNA is so often lumped with and sometimes behaves as the autosomes, it is lumped into a term atxDNA that is covered by reference here also.
The term atDNA is synonymous with the term Autosome. Because the Allosome xDNA is so often lumped with and sometimes behaves as the autosomes, it is lumped into a term atxDNA that is covered by reference here also.