On March 5, 2014 the Ancestry.com blog posted "Understanding Patterns of Inheritance: Where Did My DNA Come From? (and Why It Matters.) " by Anna Swayne.
She includes a chart that helps illustrate how different segments of DNA might have been passed down from your grandparents to make your unique DNA. I have to admit I have always had trouble grasping this concept - for the first time it finally sunk in. I found the article and chart to be very helpful.
"Your DNA contains a record of your ancestors, but you aren't a carbon copy of any one of them. The particular mix of DNA you inherit is unique to you. You receive 50% of your DNA from each of your parents, who received 50% of theirs from each of their parents, and so on. . . . .
"By understanding how DNA is inherited, you can see how and why you have some DNA segments that match your relatives, and others that do not, why you may or may not have inherited DNA segments associated with a certain ethnicity, and why getting multiple people in your family tested can help discover more of your family's genetic tree." . . . .