DNA inheritance patterns

About a dozen years ago, I read One genetic concept which completely changed my perception of ancestors is that fact you do not inherit DNA from all your ancestors.

Keep in mind that you do not inherit DNA from all your ancestors.  Ten generations ago, you have at most 1,024 ancestors; at the 20 generation level (about 500 years ago), that number is over 1 million.  It isn’t biologically or mathematically possible for you to have inherited DNA from all of those people.  Because of pedigree collapse, no one is going to have 1 million different ancestors at the 20 generation level anyway.

Generation by generation, the amount of DNA that is passed on from each ancestor becomes smaller and smaller, and at some point, can disappear.  The engine for this is meiosis, the biological process by which each chromosome is recombined during the creation of a child.  Each of your parents passes on 50% of their genome to you, but that 50% does not reflect an exact 25% from his or her parents, your grandparents.  It is jumbled and mixed up during meiosis.  Some people receive 26% v. 24% from their paternal or maternal grandparents, some receive 30% v. 20%.

Need image of recombination

In other words, there are likely going to be some ancestors at the 4GG generation level who did not contribute DNA to you.  The number of ancestors who do not contribute DNA to you increases with each generation.