16: AncestryDNA for Life Story Professionals with Scientist Mike Tones

What's the value of AncestryDNA for life story professionals? Why is one sibling’s AncestryDNA results different from another’s? If we share the same parents and grandparents, how can our tests show something different? Is genetic genealogy incompatible with family heritage? Mike Tones, scientist, explains the science behind genetic genealogy testing at sites like AncestryDNA and 23andMe. You share an average of 50% DNA with your sibling. But that’s just an average. Theoretically, you could share 100%—or 0%—of your DNA with a full sibling. Genetics and family history don’t line up exactly. In this episode, we discuss a simple overview of how genetics work, including: how DNA carries the genetic information how the DNA is packaged in chromosomes how we each have 23 pairs of chromosomes—22 pairs of autosomes and 1 set of sex chromosomes How are these genetic “packages” passed down? You don’t necessarily get 25% of the DNA from each of your grandparents because of the way the DNA is packaged. Some grandparents may be under- or overrepresented in your DNA pool. The deviation from the average gets greater and greater the farther back you go in your family tree. The “packages” of DNA in a chromosome—e.g. all of the genes on Chromosome 1—don’t get mixed up. The set of genes are arranged on that chromosome, and it holds steady. Interesting fact: By the time you get back to your great x5 grandparents, there are more grandparents than there are number of chromosomes. Genetic genealogy makes some assumptions For example: if you trace your family back to the Mayflower, that's going back nearly 400 years, or 15+ generations. The probability of you having any of the DNA of an ancestor who came over is very low. These relatives exist in your family tree, but probably not in your DNA. Genetically, you’re not like a glass of water, infinitely divisible. Because your inheritance is packaged in these chromosomes. In her Facebook group, Family History Writing and Photos, Lynn Cobine posted a message stating that the average British person’s DNA is 36% British. (One British member got results back from AncestryDNA saying she was 1% British!) What does this mean. And how are the genetic tests conducted? They don’t sequence your entire genome (yet). Mike gets into the science of genetic sequencing, explaining concepts like the double-helix, SNPs, base pair rules, and how genetic data from different populations are considered representative of certain regions. The upshot? The science is real. However, we need to bear in mind that there are certain assumptions inherent in the scientific process. A few things that genealogical genetics can show: They know the SNP markers for Neanderthals; there was interbreeding between Neanderthals and humans, and that can show up in your DNA. DNA genealogy also shows migration patterns in humans. Exchange of DNA can cross between members of pairs; it occurs during the formation of the sperm and egg. The chromosome as a completed self-contained package isn’t 100%; over time there’s a little bit of seepage between them. There are ancestors from which you will have inherited NO DNA. In the end, we’re ALL related to each other because we’re part of the same species. The nuclear genome isn't the only genome in town. Introducing the mitochondrial genome. Inside most cells are mitochondria, the powerhouses of the cell, where ATP is made. The mitochondria are derived from bacteria, which are in turn descendants of ancient bacteria. Our cells are fueled by these descendants, providing the energy they need to survive. For more on this topic, read what the Naturalis Historia has to say. The human egg is a huge cell. A nucleus and a huge amount of cell surrounding it, with the mitochondria. The sperm basically injects its DNA. That fertilized egg divides and develops, and during that process of cell division, the mitochondria are dividing as well.