top of page
  • Writer's pictureAndy Lee

Decoding Genetic Genealogy: Exploring the Math Behind DNA Matches

Have you ever wondered how it's possible to distinguish individuals from their DNA, even though we share nearly 100% of our genetic makeup? It's a perplexing question, and today we're delving into the depths of genetic genealogy to shed light on this mystery. I'm Andy Lee from Family History Fanatics, and together, we'll unravel the secrets behind DNA matches.

The 99.9% Similarity Puzzle of DNA Matches

When you contemplate the fact that we share almost 100% of our DNA, it's natural to question how we can differentiate between individuals. After all, in a crowd at a train station, you can easily spot distinctions in hair color, skin tone, clothing, and height. However, DNA operates on a different level, focusing on the underlying code responsible for these observable differences.

According to the National Human Genome Research Institute, all humans—past, present, and future—share 99.9% of their DNA. This staggering similarity is crucial to our very existence.

Without this genetic foundation, we wouldn't be the humans we are today. It's the remaining 0.1% that sets us apart, contributing to variations in traits like hair color and other distinctive characteristics.

To see the math of DNA matches, watch this video.

Decoding the 0.1%: Insertions, Deletions, and Substitutions

To understand this minute yet significant genetic diversity, we must explore the concept of single nucleotide polymorphisms (SNPs). SNPs are the genetic differences that make each of us unique, given that we are 99.9% identical to one another. These differences arise from variations in our DNA code.

Within our genome, there are approximately three billion locations, and the 0.1% variation corresponds to three million potential differences. These variations manifest in a myriad of ways, encompassing traits such as hair color, eye color, skin tone, height, and even blood type. Although the actual number of distinctions may surpass three million, let's consider this figure as a representation of the countless possibilities for diversity.

The Complexity of SNPs: Unraveling the Varieties

Each SNP consists of two letters, and there are three possible combinations between them. You can have both letters as the same type, representing "PP" or "QQ." Alternatively, you could have one of each letter, denoted as "PQ."

Thus, for every difference, there are three potential variations. Let's examine two SNPs to illustrate the magnitude of possibilities.

Considering the three varieties,

  • if the first SNP is "PP," the second SNP could be "PP," "QQ," or "PQ."

  • With the first SNP as "QQ," the second SNP could be "PP," "Q," or "PQ."

  • Even for the combination "PQ," the second SNP allows for "PP," "Q," or "PQ."

As each SNP operates independently, we uncover nine distinct possibilities with just two SNPs. Now, if we expand this to the aforementioned three million SNPs, you can begin to comprehend the enormous scope of genetic diversity.

If this explaination is clear as mud, watch the video linked above.

↪️ Are you looking for more genetic genealogy resources?

Grab our FREE DNA Related Research Guides:

FREE Genealogy Research Guide Link

The Mind-Boggling Numbers: Beyond Calculations

Let's delve into the numbers, although they may seem daunting at first. Mathematicians and astrophysicists would undoubtedly be astounded by the figure: three raised to the power of three million.

Given the three potential variations within each SNP and the three million SNPs that can differ among individuals, we arrive at an immense number. It can be expressed as a 1 followed by 1.4 million zeros—an incomprehensible magnitude.

Thankfully, genetic testing companies focus on approximately 500,000 SNPs. Consequently, we can modify the equation to three raised to the power of 500,000, resulting in a number with 240,000 zeros—a gargantuan figure surpassing any practical usage.

Narrowing Down the Numbers: The Power of Genetic Testing

Realistically, when considering any random person, you share about half to three-quarters of the SNPs with them. The degree of relatedness influences the proportion, with closer relatives having a higher shared SNP count. However, even when comparing with a stranger on the street, you still share at least half of the SNPs.

Let's refine our calculations further, reducing the number to three raised to the power of 150,000. Remarkably, we are still confronted with an astronomically large number. The sheer size of this figure surpasses the computational capacity of existing technology. Nevertheless, this vastness enables us to distinguish between individuals with relative ease.

Unmasking Identical Twins: An Exception to the Rule

One might assume that identical twins, who possess an extraordinarily high degree of genetic similarity, are indistinguishable from one another.

However, even among identical twins, there are estimated to be between five and a hundred unique mutations in their DNA at birth.

These mutations are not accounted for in standard SNP tests, resulting in identical twins appearing as a single individual in genetic profiles. For everyone else, genetic tests offer a straightforward means of differentiation.

↪️ Do you want to dive even deeper into genetic genealogy, writing family histories, and climbing your family tree? Join the

FHF Xtra Premium Membership and get a wealth of exclusive content.

Join FHF Xtra and get more access to exclusive genealogy webinars and training

The Power of Genetic Genealogy: Unlocking Our Genetic Family Tree

Considering the vastness of genetic diversity, it becomes evident that DNA testing can effectively identify and differentiate individuals. These tests become incapable of distinguishing only in the case of identical twins due to unaccounted-for mutations. Yet, for the rest of us, genetic genealogy uncovers the rich tapestry of our ancestry with remarkable precision.

If you found this article enlightening, don't miss our other captivating videos. Subscribe to the YouTube channel, or join our mailing list while picking up the free guide, 5 Most Common Questions Asked About DNA.

More Insights into Genetic Genealogy

Note: To leave a comment, you will be asked to sign in with your Facebook or Google Account. This action will help reduce spam comments on our site. I hope you'll understand.

bottom of page