In reality, the DNA segments are very seldom divided exactly in half, but all we can deal with are averages when discussing how much DNA you “should” receive from an ancestor, based on where they are in your tree.
The generational relationship chart above represents the average that you will inherit from each of those ancestors.
If the idea (that “scientific evidence must be both observable and repeatable”) were carried to its logical conclusion, it would cripple not only the study of evolution, but every line of historical inquiry.
We would, in fact, be prohibited from exploring most matters that cannot be brought inside or recreated within a laboratory, whether they be large (the composition and origin of stars, for example) or small (like the forensic recreation of a crime scene).
One of the most common questions I receive, especially in light of the interest in ethnicity testing, is how much of an ancestor’s DNA someone “should” share.
Human immunodeficiency virus (HIV) is a blood-borne, sexually transmissible virus (see the image below.) The virus is typically transmitted via sexual intercourse, shared intravenous drug paraphernalia, and mother-to-child transmission (MTCT), which can occur during the birth process or during breastfeeding.In fact, many people, encouraged by advertising, take these tests with the hope that the test will in fact provide them with the answer to the question, “Who am I?” or to confirm a specific ancestor or ancestral heritage rumor.As you can see, if you’re looking for a Native American ancestor, for example, who is 7 generations back in your tree, if you carry the average amount of DNA from that ancestor, it will be less than 1% which will be under the noise threshold for detection – and that’s assuming they were 100% Native at that time.Everyone inherits 50% of their DNA from their parents, but not everyone inherits half of each of their ancestors’ DNA from a parent.