Why You DON'T Have 25% of Grandma's Genes | DNA Inheritance Explained

Discover why you might not have fully inherited 25% of each grandparent's DNA. Genetic Inheritance is a numbers game and it can impact your genetic genealogy results.

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Chapters
0:00 - Introduction
0:16 - Understanding Autosomal DNA
0:53 - DNA Inheritance from Parents
1:49 - DNA Inheritance from Grandparents
3:04 - Recombination and Chromosome Swapping
4:09 - Different Ways of Inheriting DNA from Grandparents
6:30 - Examples of DNA Inheritance from Grandparents
7:56 - DNA Inheritance Percentage
9:00 - Range of DNA Inheritance from Grandparents
9:45 - DNA Inheritance from Paternal Grandparents
10:14 - Summary of DNA Inheritance

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✅ Let's connect:

#FamilyHistoryFanatics #genealogy #geneticgenealogy

[susanharris]

We just did my children’s DNA because my husband is half Chinese and half Western European. We wanted to see which of our 3 kids got the most Chinese because they all look very different. One is 30% Chinese, one is 22% Chinese and one is only 19% Chinese. So it’s easy to see that one child got more from the Chinese grandparent than the others did. Fascinating!

[LairdKenneth]

I am one of the few in my family that inherited my paternal grandfather's red hair (and he had ten children, so there's a lot of us). Additionally, everyone says that of all of us, I look the most like him. Though an old B&W army photo of grandpa looks more like my older brother.

On a visit to an elderly great aunt, suffering from memory problems, in a retirement home there in Clay County Kentucky, where I rarely visit, thought I was my dad. So I clearly resemble him as well.

But I also have a picture of my mother when she was a little girl, which bears a strong resembelance to me at that same age. It is amusing how these things work.

[icecoldrugby]

I'll save you 10 minutes. The half you get from each parent is a random sampling from their parents. Simple as

[LanceHall]

It took me forever to understand this until I realised it's just from the fact you are going from two person's amount of DNA to one person's amount of DNA so half of it has to be chucked out simple as that.

[kimfleury]

I just remember two separate classes in college at two separate schools -- intro to biology at my local community college, and etiology of congenital conditions when I transferred to a university to study special education. Both courses emphasized that each pregnancy is a new roll of the dice. Also, the professor in the university course was an OB/Gyn and Neonate pediatrician who ended up specializing in the care of newborns with congenital conditions. When he first went into medicine, he wondered why things didn't work out perfectly every time. Then as he studied, his question shifted to wondering why things work out ideally 90% of the time. In every case, though, you work to give the child the best chance at living to his or her highest potential.

[martheseturner]

Genetics are amazing. We have our first grandchild. I am southern european, olive skin, brown eyes, dark hair. My husband is Australian, with the usual English, Irish & Scottish background. However he too is olive skinned & brown eyed, although his skin colour is lighter than mine. Our children are a mix of the both of us. Our grandson is extremely fair skinned, blonde haired & blue eyed. He's just like his mother's side in colouring. They are all fair skinned & blue eyed.

[waterwoman]

Always remember, the percentages inherited are AVERAGES. ON AVERAGE 25 percent from each grandparent, but not everyone will actually have 25 percent

[bobkelley]

You did not even mention the the mailman 😄 Thank you very much.

[chrisper]

I saw another video where the claim was that the further back the relationships, the less we inherit any of their DNA. But, it’s better to say that the DNA chromosomes can rearrange themselves to complete the DNA strand, meaning that the contributions from far distant contributors can come to the fore as needed. It’s like a numbers shuffle.

[loislewis]

Both my parents immigrated to America, therefore I did not grow up with either side of the family. I had spent more time with my mother’s family but did not feel particularly close to them. But when I finally met my father’s family there was an instant connection, similar sense of humor, similar occupations. I guess it was in the genes 😅

[vanhetgoor]

I still love both of my late grandmother's, I carry their remembrances in my heart.

[lauraneville]

excellent explanation! thank you so much!

[cipriantaoshu]

I share 50.8% with my father and 49.2% with my mother. I also share 27.8% with my grandmother from my mother's side and 22.2% with my grandfather.

And 38.2% with my brother.

[paulwetzel]

My wife’s grandmother is Okinawan. She has 23% southern Japanese islands DNA.

[johnpowell]

That's a good explanation.
Note also that for most folk, the 25% story is considered at the phenotype level which correspond more strongly with genes than chromosomes. If you do the analysis at the gene level, similar considerations to chromosome level apply, although recombination plays a smaller role so the 'all or nothing' occurrence is more frequent. There's a lot of non-coding DNA and this no doubt has some effect on phenotype; similar inheritance considerations probably apply.
At the level of single nucleotides, the transmission is almost 100% all or nothing because recombination does not apply, only the very rare mutation event.

[Legless_Orphan]

Genetics are a fun topic to learn about.

My grandmother had 4 children. All had different hair colors but all were born with blue eyes.

[PS-qnoz]

Wow, thanks for clearing this up. My family's DNA results were shocking and revealed that my maternal grandfather was not our biological grandfather. My mother and her parents are deceased and so far there's no way of knowing who exactly my grandfather was. Yet I have 28% of his DNA.

[tammyhall]

I come from a family of over 30 1st cousins. I am the only one who inherited my Grandfather's grey eyes. Neither of my siblings or parents got them either. I look pretty odd in a prominently Filipino family with red hair and pasty white skin !!!

[melodywolff]

A simple example to compare to is flipping a coin 22 times. If you had to put money on what the outcome would be, you'd put money on 11 heads and 11 tails. However, if you had to put money on whether or not you'd get 11 heads, you'd always bet against that. Of course crossover makes the math for genes less neat, but still, the simple example is perhaps a good way to get people to understand.

[yessumify]

My husband is Mexican, my ancestors are from England and Africa. We had a baby 5 days ago with blonde hair and light skin. Genetics are awesome! We named him after my Dad, the og blondie. <3 :)