Question 11.10

Q: Are clues to your ancestry hidden within your DNA? The short answer is yes. Researchers use comparisons of DNA sequences to explore personal ancestries within our species, even preparing pie charts that purport to identify a person’s ancestral proportions (for example, 10% West African, 70% Middle Eastern/North African, and 20% European).

Question 11.11

Q: How is DNA used to build a family tree? Most tests are based on one of three types of analysis. (1) Mitochondrial DNA tests evaluate highly variable sequences in maternally inherited mitochondrial DNA. (2) Y-chromosome tests look at variation in the paternally inherited Y chromosome. (3) Autosomal DNA tests examine highly variable sections of DNA scattered throughout the chromosomes. In each case, a sample of cells is collected (usually by swabbing the inside of the cheeks), then technicians determine the base sequences at a number of locations (a few dozen to several hundred) and compare those sequences with sequences from thousands of individuals in populations around the world. The matching of your sequences with those of other samples is then interpreted as potential evidence of shared ancestry.

Question 11.12

Q: Genetic ancestry testing may be good fun, but is it good science? Unfortunately, the limitations of commercially available tests of genetic ancestry are significant. These are among the most important limitations:

• High genetic variation among individuals within most populations makes it difficult to identify specific sequences that can reliably indicate membership in a population. As an analogy: if Native Americans are highly variable for a trait (e.g., height), we can’t use that trait to prove someone’s Native American ancestry.
• High rates of gene flow between populations reduce the reliability with which any sequence can demonstrate membership in one particular population. As an analogy: dark hair is extremely common in Asia, but having dark hair doesn’t necessarily indicate Asian ancestry.
• Evaluating too few genetic loci, of which just a small number happen to be similar, can lead to the conclusion that individuals are much more genetically similar than they actually are.
• A DNA match between two individuals living today is not a match with an ancestor. Rather, it suggests that the two people may have inherited the DNA sequence from a common ancestor.

Question 11.13

Q: What can you conclude? Until we have a much more comprehensive catalog of genetic variation—including precise estimates of how much variation exists within populations and how much exists between populations—the results of genetic ancestry testing remain overly speculative and insufficiently reliable. Conclusions may be incorrect and misleading. But, because the conceptual underpinnings are solid, the future of genetic ancestry testing is promising.