how are percentages of dna passed down
In general, you share an average of 50% less DNA with an ancestor with each additional generation. To find how much DNA you likely share with a cousin, consider that they have also inherited 50% less DNA with each generation. A modified version of the genealogical relationship chart shows this. For example, you and your relative share a common ancestor, Emmet Wiscured. Emmet is your 4th great-grandfather.