It is hard to conceptualize that our ancestors live within us. At least on the genetic level it is the fact that we carry [hopefully alive] parts of our past generations in our genes. Now a "gene" is the functional unit of heredity which occupies a specific place (called locus) on a chromosome. This gene is capable of reproducing itself exactly at each cell division, and directs the formation of a protein. [ an enzyme, a catalyst, or other types of helper proteins ] A "chromosome" (normally 46 in us humans) lives in the nucleus of our cells. It is the bearer of our genes, but also surrounds itself with specialized filaments [called chromatin], and a helper gizmo that assists during cell division called the centromere. Concepts, terms, definitions and the like surrounding all this genetic stuff can certainly clog the brain, and may often form their own brick walls just trying to put things together. Anyway, to help the genealogist in their own tree climbing experience there are a few themes that might provide some insight.
First, "genetics" and "genealogy" are not the same. In spite of what is claimed from all those who want to sell DNA products in order to provide you with answers to all your family tree questions, this is not the case. By definition, "genetics" is the branch of science concerned with the means and consequences of transmission and generation of the components of biological inheritance. In my Stedman's Medical Dictionary, between "behavioral genetics" and "transplantation genetics" there are 21 definitions of various branches. By definition, "genealogy" is an account of the descent of a person, family, or group from an ancestor. [There is now listed a "genetic genealogist" which I am sure would charge you to figure all your DNA stuff that has been analyzed.]
Secondly, if you have not already, you may discover that your DNA may help get under, around, or over that brick wall. The problem for many genealogist is knowing which DNA type would give you the most help. The following picture tries to present the three types of DNA being sold on the market.
The first place to start is to define the question you are trying get hold. [From a genealogist point of view.] Does the question needing to be ask go out the paternal (fathers) branches, the maternal (mothers) branches, or the ancestors on either side of the family tree? Making this decision will often help you decide which DNA test to order. Y-DNA is a direct male line back through the ages...mtDNA (mitochondrial DNA) is down the maternal branches including those of your father...and autosomal DNA is basically a "travel log" of your ancestors geographic origins. [called ethic groups] We all have genes...well traveled indeed.