What can DNA tests really tell us about our ancestry? - Prosanta Chakrabarty

Summary

DNA tests can reveal insights into our ancestry, but they have limitations. Two sisters may show different results despite sharing the same parents due to genetic recombination, which mixes the DNA inherited from each parent. These tests compare a person’s genetic markers to those of modern populations, like those living in France today, rather than tracing specific ancestors. The underrepresentation of certain populations in genetic databases also affects the accuracy of results. As genetic testing evolves, results may change, highlighting the complexity of tracing ancestry through DNA.

Takeaways

• 😀 DNA tests can provide surprising results, such as one sister being 10% more French than the other, despite having the same parents.
• 😀 Commercial DNA tests use less than 1% of the 1% of our DNA that varies between individuals, which leads to some unexpected results.
• 😀 DNA tests rely on genetic markers, which are short sequences found in specific places in the genome, to trace ancestry.
• 😀 Recombination is the process where chromosomes swap parts before forming sperm and egg cells, making each individual's DNA unique.
• 😀 While you inherit half your DNA from each parent, recombination makes it difficult to predict how much DNA you’ll inherit from distant ancestors.
• 😀 The amount of DNA inherited from each ancestor decreases with each generation, and some ancestors may not appear in your DNA at all.
• 😀 The French ancestry detected in one sister’s DNA may not represent actual French ancestors, but rather shared genetic markers with people living in France today.
• 😀 DNA tests assume that shared genetic markers with people from certain regions indicate ancestral connections, but these assumptions may not be entirely accurate.
• 😀 The results of DNA tests can change over time as more people have their genomes sequenced, especially with an expanding database.
• 😀 DNA tests cannot trace heritage from people not represented in the database, and they should not be used to define race or ethnicity.
• 😀 The 2% Neanderthal DNA found in some humans is part of the 1% of DNA that varies, showing how interbreeding with Neanderthals left a genetic legacy.
• 😀 Because of the complexity of DNA inheritance and the available genetic data, tracing ancestry through DNA testing is not always certain.

Q & A

Why do two sisters taking the same DNA test have different percentages of French ancestry?

The difference arises due to the random nature of recombination in the inheritance of DNA. Even though they share the same parents, the genetic recombination process can result in one sister having a higher representation of French ancestry in her DNA than the other.

What is the process of recombination in genetics?

Recombination occurs when the chromosomes in sperm and egg cells swap sections, creating a unique mix of genetic material. This process ensures that each sex cell carries a distinct combination of chromosomes, which leads to genetic diversity in offspring.

How much of our DNA is shared among all humans?

99% of our DNA is shared among all humans. The remaining 1% contains the genetic differences that distinguish individuals from one another.

How do DNA tests determine ancestral origins, such as being 10% French?

DNA tests compare an individual's genetic markers to those of people from specific regions, like France. If an individual shares certain genetic markers with people in France today, the test assigns a percentage of their ancestry to that region.

Why don't DNA tests trace the exact ancestry of an individual’s ancestors?

DNA tests cannot trace the DNA of deceased ancestors because we don't have access to their genomes. Instead, they compare an individual's genetic markers to those of present-day populations.

What is the significance of genetic markers in DNA tests?

Genetic markers are short DNA sequences found in specific locations on chromosomes. DNA tests use these markers to identify shared genetic traits with people from certain regions, which can then be used to infer ancestral origins.

Why are many indigenous populations underrepresented in DNA testing databases?

Most DNA testing databases have a higher representation of individuals of European descent (80-90%). As a result, the genetic contributions of indigenous peoples and other underrepresented groups are less likely to be reflected in the results.

How might DNA test results change over time?

As more people participate in DNA testing and databases grow, the accuracy and scope of ancestral estimates can improve, which might lead to changes in an individual’s results over time.

How can someone be both 100% French and have 2% Neanderthal DNA?

Since Neanderthals were a separate species that interbred with early humans, their genetic contributions are found in many people's DNA today. The 2% Neanderthal DNA comes from a distinct part of the genome that does not conflict with being 100% French in terms of modern ancestry.

What is the 1% of our genome that varies, and why is it important for ancestry testing?

The 1% of our genome that varies contains the genetic differences that contribute to traits such as ancestry, ethnicity, and individual characteristics. This 1% is what DNA tests analyze to determine your ancestral origins.