Autosomal DNA refers to the twenty-two pairs of non-sex chromosomes found within the nucleus of every cell. The first forty-four chromosomes are called autosomes. The twenty-two autosomes, or autosomal DNA chromsomes are numbered approximately in relative to their size, with autosome 1 being the largest and autosome 22 being the smallest.An autosomal DNA test identifies shared segments of DNA across the first forty-four chromosomes. When you and another person share a significant amount of DNA segments across your autosomal chromosomes, then you and that person have a common ancestor in your respective pasts.
The DNA amount, size, and segment length is represented as a unit of measurement known as the centimorgan (cM).
An autosomal DNA test uncovers and reveals relatives (matches) on both sides of your family in a genealogical time frame.
It is from that ancestor that you and your match received the shared DNA segments.
Example of the use of mtDNA testing to determine ancestor relationship. click on example below, from Ancestry.com DNA my testing results