Y chromosomal testing is particularly useful for several reasons.
Because it includes the
Here's a fan chart I found on the web years ago. It should illustrate the point:
Follow the bottom rib along the paternal Griffin line to the left and the
maternal lineage and its ever-changing surnames to the right. The DNA
fingerprints will match for each person along its respective arm. From this
graphic, we can readily see that genetic information for the other ancestors
cannot be gleaned from the
Every one of our cells contains 23 pairs of chromosomes, the most
famous of them being the so-called
A set of autosomes comes from both parents, each comprised of a single
set of
Autosomal tests look at about 700,000 base pairs. These particular bases are selected primarily because they tend to have a degree of variability. (Without variability, we'd be unable, naturally, to see genetic differences.) However, it's impossible to determine which bases came from which parent only by looking at the results. They're not marked "this one came from your dad and this one came from your mom." Progress cannot be made without comparing the results among individuals. The larger the database, the better.
DNA testing companies do most of the work for you by sorting, evaluating, and displaying your matches. Your results are compared across their entire database. They determine the size and number of matching segments, arrange them from the best matches to the poorest, and determine a range of possible relationships.
FTDNA's autosomal product is called Family Finder ($99). Here are my top matches (minus the names of the matching individuals):
And at 23andme:
"cM" stands for
As mentioned, we inherit half of our autosomes from each parent. A quarter, therefore, comes from each grandparent and an eighth from each great-grandparent. But which chunks of DNA came from whom? We can know that only by comparing to other testers. My sister and I share a quarter of our DNA but there's nothing in the results to tell us from which parent the various bits were inherited. Clues are present in the DNA results of our maternal half-sister because we share DNA with her only through our mother. Identifying maternal markers helps to determine which side of the family a distant cousin comes from. The same can be accomplished with any close degree of relationship.
Because DNA from any one ancestor halves with each generation, relatively
few generations pass before what remains is so minimal that the chances of
finding a match becomes remote, particularly considering that any two
distant cousins might have inherited entirely different strings of bases
from the mutual ancestor. Therefore, autosomal results are typically
reliable to only about five or six generations. Nevertheless,