DNA is not lost to recombination if you have long lines of male or female ancestors. It can be passed down IBD for many many generations. The other factor of preservation is when you have the same ancestral line more than once or both of your parents share a common ancestor. DNA gets crowded out by other DNA and does get lost if you do not have more than one line related by that surname and it goes too far back. My most recent Bryan is Hannah McDaniel Bryan. She is my 4th GGM. My Genesis match is a direct descendant of Morgan Strode Bryan. Our common ancestor is Sir Francis Bryan. Of my other DNA matches with other people besides my cousin who descends from Morgan Strode Bryan, I have as common ancestors: Sir Francis Bryan III, b. 1630, married to Sarah Brinker. NOT BRUNGER. Sir Thomas Bryan II, K.T., b. 1464, Sir Francis Bryan, Vicar of Hell b. 1490, and William Smith Bryan b. 1599. The amount of DNA shared is dependent on the common ancestor. These common ancestors were all born over 300 yrs. ago, so the DNA segment is going to be consistent with that time range. End location numbers are relevant to both surname and Haplogroup. Haplogroups don't disappear, What happens is that markers associated with haplogroups mutate over long periods of time. By the same token, your AT DNA will only disappear if you don't marry back into the same line at some point or your ancestors get crowded out when other descendant's who have long lines or multiple lines of an ancestor to take up real estate on your chromosomes. Your 23 chromosomes can only hold so much information and every end location number you share with another person represents an ancestor in common. The current thought is that DNA is divided in half each generation back getting smaller and smaller and they tell you that after so many generations you won't be able to find it and it becomes noise. I oppose that analogy because it is ridiculous. If you could bring back an historical person born in 1500 today, you cannot say that they are nothing but noise and do not exist any more than you can say that you are noise and do not exist to your 10th GGS. Everything leaves a print.