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Mr. Gregory White
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Can a person be 70:30 say Irish:Russian or whatever,

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Can a person be 70:30 say Irish:Russian or whatever, or does it always have to be 75:25 because of the math of having 2 parents, 4 grandparents etc?

Hello and thank you for using this service. I am a Research Librarian with over 10 years of experience.

You can absolutely be 70:30 ethnicity. The 75:25 formula is in play only if the direct ancestors before you were say 100% and 50% of an ethnicity respectively. You are half of whatever your parents were and they half of theirs, and so on. Unless every person marries someone who is 100% one ethnicity or 50% another (or 25% or 75%), those percentages will not always be in quarters. The further back you can get in your family tree or bloodline, the more variables may come into play concerning your ethnicity.
When generations proceed with people marrying outside of their own ethnicities, those percentages will go down naturally because the ethnicity can get more and more diluted in the bloodline as the family line continues. It is entirely possible to be 70:30.
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Customer: replied 4 years ago.

I tried to do the math to prove it and could not. 2 parents, 4 grandparents, then 8, then 16 etc etc. I thought I needed to find a number that is to the power of two, but also divisible by both 7 and 3 for the hypothesis to be correct. Please can you help with me with a mathematical answer? Thank you.

For some reason, my previous answer did not post. I was thinking we were speaking in more general terms where someone is 30% (but really is just "about" 30%) and I was more focused on the "does this HAVE to be a quarterly measurement?" part of your question. You can be 5/16ths of an ethicity and then 31.25% which is the closest I could come.
As I am certainly not a math expert and you desire a more mathematically focused question, I will opt out and see if another more math-minded expert can expand on this.
Customer: replied 4 years ago.

Thank you for that, sorry, I should have been more mathematical in my first question (though that is why I posed my question to a math expert originally!) Shall I wait to hear from someone else, or should I re ask the question? Thanks so much for your help, Helen

I have already asked the moderators to repost for you and I specified that you required a math expert. It popped up in the general feed which is how I found it. No need to do a thing and hoping a math expert will get to you soon. Thank you for your patience!
Customer: replied 4 years ago.

Thanks so much!


Just wanted to interject that there is little likelihood of finding a mathematical formula unless all of your ancestors are 100% of either Irish or Russian extraction. So far, I've never come across such a family.


How about the grandmother whose maternal parents were from Germany and Russia and her paternal parents were from Australia and Ireland? Or the grandfather whose parents were from Scotland and Brazil on his mother's side and Ireland and Scotland on his father's.


Best regards,






Customer: replied 4 years ago.

What I would like to do is just prove that it is possible to be 70:30 of some combination. If I could find one example where the math works, I would not care about the permutations/mixes historically. It need not even be realistic, just possible. My hypothesis, which I need to prove, is merely that it is a possibility, I am just not sure how to show that it should be technically/mathematically possible. Thank you.

I think I understand. However, with genetics, it has to be realistic and possible. Anyone can put together a formula that results in a 70:30 mix if there are no constraints on what is possible to happen.


You might be better off asking if it is possible to get a 70:30 mix of white and blue marbles.


Customer: replied 4 years ago.

I guess what I was trying to say is that I was just looking at it mathematically - the other side in the discussion was telling me it had to be 75:25 and could never be 70:30, so I do not mind what assumptions or parameters are used, I just want to get to where I can show that a 70:30 mix is theoretically possible.

I have asked to have your question moved to Math Homework. That is where all the mathmeticians are.
Customer: replied 4 years ago.

Thank you - that's where I originally posted it! :)

Hello, my name is XXXXX XXXXX I am happy to help on this question.

Let me take a look at the math side of this and will get a response back to you this evening regarding this possibility.


PS - I have taught math and probability for 15 years.
Customer: replied 4 years ago.

Thank you - I will look forward to hearing from you!

No problem - give me just a couple hours till I can really sit down and think this one through.
I have run the numbers here and there is no way that you could be 70% and 30% of only 2 specific ethnic populations. However, you could be 70% and 30% of different populations such as European (as that is made up of many different specific ethnic groups) or African (since there are so many different groups of African that make up the group.

However, taking only 2 specific groups, we cannot break it down through generations unless you are to go back well before those countries even existed.

Each parent would be 50-50, each grandparent would be 25-25-25-25, each great-granparent would be 12.5-12.5-12.5-12.5-12.5, etc. This keeps breaking down as you go back generations but there was nothing that would add up to a 70-30 split going back the generations.
Mr. Gregory White, Teacher
Category: General
Satisfied Customers: 5240
Experience: M.A., M.S. Education / Educational Administration
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Customer: replied 4 years ago.

Thank you so much for that, though I was hoping it could be proved! Thanks anyway though, now I know!