Via https://blogs.ancestry.com/ancestry/2014/03/05/understanding-patterns-of-inheirtance-where-did-my-dna-come-from-and-why-it-matters/ – Ancestry.
The chart below helps illustrate how different segments of DNA might have been passed down from your grandparents to make your unique DNA. Assume each letter represents a segment of DNA. Things to notice are:
- Which letters get passed down to each generation is random (the fact that the letters spell names in this example is simply to help with the illustration).
- Not all of the letters get passed down.
- Just because a child doesn’t have a letter doesn’t mean that an earlier ancestor didn’t have that letter.
- Siblings can have different combinations of letters
One of the easiest explanations of how DNA can be passed down to succeeding generations I have come across.
Ups Downs Family History 