Skip to Content

Does DNA Get Washed Out Over Generations?

Does DNA get “washed out” over time? If it does, how does the process work? In this post, you will find the answers to these questions, plus:

  • How many generations does DNA go back
  • How much DNA you inherit from your ancestors
  • Whether DNA can skip a generation

On DNA discussion boards, I see the expression “washed out” or “watered down” used frequently when people discuss why someone might not have inherited an ethnicity region from an ancestor.

It is also used to describe the common situation where two distant cousins share no genetic material.

Does DNA Get Washed Out Over Generations_

Is it true that DNA from your ancestors gets washed out over time?

While DNA doesn’t truly “wash out” in a literal sense, DNA passed down our ancestors was “diluted” with the DNA from other ancestors. In this way, it is true that genetic material from distant ancestors is “watered down” over time and will not show up as intensely in our DNA results as DNA from our recent ancestors.

For example, if I know that my 6th great-grandmother was Irish, I might be expecting to see a certain percentage of Irish DNA in my ethnicity estimate (or ancestry estimate, as it is sometimes called). If I don’t see any Irish in my results, I can assume that the amount of Irish DNA that I inherited from her was too small to show up in my results.

In other words, the DNA that my 6th great-grandmother passed down to her child (my ancestor) was mixed with other DNA each generation, effectively “washing out” by the time it got to me.

Click here to buy the Understand Your DNA Results Ebook

How does DNA “wash out” over time

If it’s true that DNA can get “washed out”, how does this process occur? It happens through a process called “recombination”.

Every child inherits 50% of their DNA from their mother and 50% from their father. The DNA passed down from their parents is in the form of one copy of each of their 22 chromosomes from each parent, and a sex chromosome from each parent.

To make this explanation simpler to understand, let us narrow our discussion to the DNA that a child inherits from their mother. For this purpose, the process is identical to DNA inherited from the father, with the single sex chromosome being the exception.

Each chromosome that the child inherits from their mother will be a “recombined” version of their mother’s two copies of that chromosome. For example, your mother has two copies of Chromosome 1, inherited from each of her parents (i.e. your grandparents).

When you were born, you got a copy of Chromosome 1 from your mother and another copy from your father. The copy of Chromosome 1 that you got from your mother was made up of a mixture of your mother’s two copies of Chromosome 1.

how recombination works to make a new copy of a chromosome
On each chromosome, the same thing happens. Mom and dad both have two copies of each chromosome. Their two copies recombine to make two new, completely unique copies to pass down to us!

The recombination process, which can be imagined as “mixing” two copies of the same chromosome, randomly chooses pieces of DNA from each copy to create a brand-new, completely unique copy of that numbered chromosome.

These “pieces” of DNA that form our new copies of our chromosomes are made up of smaller pieces of DNA called DNA segments. These DNA segments were inherited from our more distant ancestors.

Since the size of Chromosome 1, and every other chromosome, is limited, the mother can only pass down 50% of her two copies of Chromosome 1 to her child – i.e. you. This is how some DNA is “lost”, or “washed out”, over time – some DNA is not passed down to the next generation.

The process of recombination occurs each generation, with DNA being randomly selected to get passed down. These are the events that create our completely unique genome.

The visualization below is a simplified example of how the DNA that two first cousins sharing two grandparents inherited vastly different DNA from their common ancestors. It should help you understand how some ethnicity regions, the top reason that people are curious about DNA being “watered down”, disappear from DNA over time.

A visualiation of how ethnicity is passed down in DNA

Imagine that Nicole and James start their own families and the trend of DNA inheritance continues. How much DNA will their children share with the grandparents of Nicole and James? How much DNA will their descendants share with each other?

How many generations does DNA go back?

Since now we understand more about how DNA from some of your ancestors really does, get washed out or watered down over time, the logical question to ask next is:

How many generations back does DNA go?

There is no hard and fast answer that applies to everyone, but there are a few things that we do know for sure. For example, we will always inherit substantial percentages of DNA from:

  • parents (50%)
  • grandparents (about 25%)
  • great-grandparents (about 12.5%)
  • great-great grandparents (about 6.25%)
  • great-great-great grandparents (about 3.125%)

Going back further than great-great-great grandparents, we should understand that while we inherited DNA from many of those ancestors, the size of the segments and amount of total DNA inherited from any given distant ancestor will vary greatly.

At a certain point, it is theoretically possible to have inherited no DNA from any given distant ancestor.

For example, there is about a 5% probability that you will share no DNA with a great-great-great-great-great grandparent. This might initially seem odd – how can you possibly not have inherited DNA from an ancestor only seven generations back in your tree?

When you imagine that you have 128 great-great-great-great-great grandparents, it might be easier to visualize how mathematical probability and the limited size of the human genome affects percentages of DNA shared with these ancestors.

Can DNA skip a generation?

If you didn’t see what you were expecting in your DNA results, you might wonder if the ethnicity region perhaps skipped a generation.

In reality, it is not possible for DNA to skip a generation. 100% of the DNA that any given person has was inherited from either of their parents, which means that we can’t inherit any DNA that our parents didn’t have.

The same is true for any other generation in our ancestry. For example, our parents couldn’t pass anything down to us that their parents didn’t have, and

Conclusion

I hope that this post helped you learn more about the concept of DNA getting “washed out” or “watered down” over the passing of time and generations.

If you have any questions about something that you read in this post, or would like to share your own experience about DNA being “watered down”, I would love to hear from you in the discussion below.

Thanks for stopping by today!

Share the knowledge!

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Patricia Damiral

Friday 25th of March 2022

I thought I would have Irish DNA as both my mother and my grandfather were Irish. Why do I not have any?

Mel

Sunday 16th of January 2022

Hi, Thank you for this article. It is one of the most insightful I have found. I have a question about one of things you wrote -- we can’t inherit any DNA that our parents didn’t have. I have a lot of DNA ethnicity that my parents don't have, and this is after all 3 of us have taken the Ancestry DNA test. They both matched as my parents, but the ethnicity was odd. For example, my mother has 11% Germanic Europe, my dad has 26%. So I would think I would be around 18%, but instead I have 42%. I have 8% from Wales, and my parents both have 0%. Norway and Ireland are the same thing where I have a small percentage and both parents have 0%. So I am not understanding how that would happen if DNA ethnicity doesn't skip a generation and we can't inherit DNA that our parents don't have. One thing to note though is that about 30% of my family tree was born in the United States since the 1700s. It doesn't appear to show up in Ancestry (and we aren't Native American), so could this throw off the results?

Thank you!!

julie

Sunday 26th of December 2021

this explains to me why i look like a certain ethnic group but it all does not show up in my an cestery. thx. for clearing this up. i have more reserch to do!

Mercedes

Thursday 6th of January 2022

I am so glad that this article helped. Best of luck in your continued research! Sincerely, Mercedes

Sofia

Sunday 5th of December 2021

Your article is very helpful. But I am still confused about some of my findings in my DNA test and I would love to know your opinion on the matter. I descend from Italians. My great grandfather was born in my country, but both of his parents were born in Italy and came to Brazil already married and with other children. So from your explanation I understand I should have around 12.5% Italian ancestry. For the rest of my father's family we know most of them came from Portugal (but actually have been for many generations in Brazil, so we always expected that there could be a mix there). And then there is my mom's side which we know came all from western Germany (with some very distant ancestors from nearby regions like eastern French border, Luxembourg and maybe Austria). I have done a lot of research and have documents that back up all this information. Also obviously a lot can be confirmed by my grandparents about their German/Italian ancestry (as their own grandparents were the immigrants). Now... I understand that there can be some mistakes in the result with a lot of people being assigned to odd ethnicities that don't match what they actually are. The problem is that my DNA test came back as 47% Northern/Occidental Europe (Germany, eastern France, Austria, Switzerland, Belgium, Netherlands), 30% Irish/Scottish/Welsh, 11% Balkans and some other small things (northern African and occidental Asian). There is nothing of Italian or Portuguese in my results. Could that be a mistake? I did my test with MyHeritage and I now regret it because it seems other companies have more comprehensive/precise results (and maybe better database?). I come from a region with a lot of German/Italian/Portuguese immigration. There were also waves of Polish, French, other Eastern Europe groups, Japanese immigrants at some point in history... but not Irish/Scottish/Welsh... I am asking your opinion because I know very little about DNA tests and I don't feel comfortable asking my family about this. I got matched by the website with a few cousins from my mom's side, but not from my father's side (but I don't even know if anyone has ever made any test as well). So would you think that it could be a mistake? Just a flaw in the algorithm?

Janine Robidoux

Monday 29th of November 2021

According to the results from 23$Me, my husband and I are 4th cousins. I am curious about how that happened. Also my granddaughter has 31% of my DNA instead of 25%.

This site uses Akismet to reduce spam. Learn how your comment data is processed.