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Thread: The risky life of my Y-DNA

  1. #1
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    Lightbulb The risky life of my Y-DNA

    Hi forum!

    Looking at my own male ancestor line, it occured to me how fragile it was and how quickly different male branches died out. I then decided to use my limited skills in statistics to have a look at it, and the result was quite surprising!

    The logic goes like this: I have two children, a son and a daughter. Applying crude statistics, that is just as it should be, if one considers the chance og having a girl og a boy as 50/50 (I know it is not excactly like that in real life, but its close!).

    My Y-DNA is lost with my daughter, no matter how many boys she might get, my son is my Y-DNA's only hope for survival! Now lets assume that he also goes for just two children - the odds that he will have only girls is 25% (0,5 x 0,5) and the odds that he will have one or two boys is 75% (1 - 0,5 x 0,5). If the next generation also aims for 2 children, odds are once again 25% and 75%. But this brings the odds of my Y-DNA surviving yet another generation in a direct male line down to 0,75 * 0,75 = 0,56 = 56%. And so on...

    Using a spreadsheet, I made these calculations to see the odds of my Y-DNA surviving a certain number of generations, assuming a given number of children that grow up and get the same number of children themselves and setting the boy/girl ration at exactly 50/50.

    The numbers are interesting - or did I miss something in my calculations?

    This also explains why some haplogroups are so big - the men who get a lot of children simply win the Y-DNA race!

    Ydna_survival.png

    EDIT: OK - I am not the first one wondering about this: https://en.wikipedia.org/wiki/Galton...Watson_process
    Last edited by A.Morup; 04-01-2017 at 03:52 PM.

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  3. #2
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    I have three male cousins who have the same surname and hence the same YDNA as I do. Between them they had seven children. All seven are females. I could go on. Our YDNA ine produced numerous males in the previous couple of generations, but it is now about to expire.

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    Thanks for doing those calculations, they're certainly interesting to see and quite alarming in a way when you realise how quickly a Y-DNA line can die out.
    Paternal Y-DNA: U152>L2>BY3508>L135>BY3506 Estimated age of BY3506: 500BC
    Most Distant Known Paternal Ancestor: Patrick Dillon, born around 1790 somewhere in Ireland (possibly County Mayo). Some of his descendants later moved to Manchester, England between the 1820s and 30s.

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    Quote Originally Posted by GoldenHind View Post
    I have three male cousins who have the same surname and hence the same YDNA as I do. Between them they had seven children. All seven are females. I could go on. Our YDNA ine produced numerous males in the previous couple of generations, but it is now about to expire.
    How do you know it's about to expire? You've mentioned three male cousins with only female children. Are these 1st cousins? Then how about 2nd cousins? 3rd? 4th? How far back can you go before the precursor of your Y chromosome isn't substantially equivalent? If you don't know that, you can't really say whether your Y chromosome is "about to expire".

    But will it do so eventually? Almost certainly, if only through the eventual accumulation of mutations -- no matter how far down it might be passed. After all, it's hypothesized that every Y chromosome that now exists could be traced to the same man -- the misleadingly-named "Y Adam".
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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    As a matter of curiosity, this caused me to do a little backtracking of my own Y chromosome. I have only a daughter, but each of my two brothers has one son. One of the sons also has a son.

    My father had five brothers, plus a paternal half brother who is a couple of years younger than I am. I think the five acknowledged brothers each has one son, and more than one of the sons also has at least one son each.

    In addition to this, my grandfather had two brothers. Each of them had sons, and I think there are some grandsons in my generation. I don't know how many.

    My great grandfather had no brothers who survived to adulthood. In fact, he only had one sister who did. But, his father had one brother, and it looks as if there was one son in each generation until my own. In that generation, there are three sons. (And I should note that I'm only considering patrilineal lines here.)

    There appear to have been at least three sons in my 3rd great grandfather's generation -- including him. As I said, my 3rd great grandfather himself only had two sons, though both of these had sons. One of my 3rd great grandfather's brothers had at least four sons, and there are some patrilineal descendants of at least my generation. The 3rd brother had at least one son, and there were patrilineal descendants to at least my father's generation, but I don't know whether there are any in my own or beyond.

    My 3rd great grandfather's father was one of 5 sons. I don't know much about the descendants of most of these, other than those of my 4th great grandfather. However, one patrilineal descendant of one of the other sons matched me on 46 out of 46 markers on Ancestry's old Y DNA test. He was not of my generation, but my grandfather's generation, and had been lieutenant governor of Delaware. As I said, he had a genetic distance from me of 0 out of 46 markers, and I suspect there would be few other differences on our entire Y chromosome -- and this is someone who'd be a 4th cousin twice removed to me.

    So, I suspect my own Y chromosome is currently in very little danger of going extinct, even though there are only a few hundred people in the world with my exact surname. (There are also several variants of the surname, whose males likely all share near-identical Y chromosomes.)
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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    I have been blessed with two sons, and my youngest son has two sons of his own. A second cousin who is a 111/111 match for me has four boys of his own. I'm not sure how many others in our y-dna line there are out there, but this thread has made me curious. I have quite a few matches with my surname and the Stephens variant of it.

    In honor of Lon Chaney Sr.'s birthday today:

    y-dna line to preserve.jpg

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    Hi there!

    Thank you for the many comments!

    Please be aware, that I am not 100% sure that my calculations are right!
    And even if they are, remember that I look downstream from myself - the calculations are the odds that my personal Y-DNA will survive.

    When it comes to other living people with the same Y-DNA as me, that is a different story. I have made a special "Y-DNA tree" for myself. It starts with my most distant known male ancestor (born ~1655) and then follows only male lines downstream. That was when it occured to me how fast male lines have died out in my line. Not necessarily in the first generation, but then after one or two more...

    And for those of you, who have taken BigY and are lucky enough to have one or two close BigY matches, have a look at this project of mine that mixes the fields of male line genealogy and "private" SNP testing: http://www.anthrogenica.com/showthre...te-SNP-project

    When it comes to Y-DNA it all comes up to how you see the world:
    - Looking backwards, every human has a direct male line
    - Looking forewards, it is very unsure whether you will have a male line or not

    Kind regards
    Anders

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    Having only two children is a pretty recent change in the number of children per couple. During the 1700s and 1800s, the families were much larger. However, your math will be more representative of many generations to come. There are some exceptions even today where birth rates are much higher: 1) LDS and Catholics are encouraged to have large families (although Catholic birth rates are declining from the past); 2) immigrant families from Latin America to the US continue to have large families (similar to my recent ancestors and the Catholic influence); 3) African Americans used to have very large recent families but their birth rates are greatly declining as well.

    Also, there have been periods of very high mortality rates in specific areas. Ireland has many of these periods in the recent past: 1) potato famines of the mid 1800s; 2) the great crop failures of the 1740s (my Caseys came to the US then); 3) invasions of the Vikings, Danes and English; 4) intense warfare from many regional kings to all of Ireland under the Dal Cais (L226) and O'Neill (M222) at the expense of their neighbors; 5) the great plague; 6) and during the last great Ice Age the population of Ireland went to zero since it was under a couple of miles of ice.

    So, birth rates and death rates varied significantly which is a major factor. There was an article some time ago that stated that over 90 % of all our male ancestors have no living male descendant today. My great grandparents on my Shelton line have no male descendants yet have over 500 descendants. However, his parents have at least 500 male descendants that I have compiled. So with one generation, no male descendants to probably 1,000 male descendants. Statistics can have some pretty severe variations due to the bell curve.

    I completed my "Olliff Family History" book around 25 years ago. This surname is unique to one male ancestor in the mid 1700s in the southern US. I was very lucky to be able to document 90 % of the descendants for the first four generations and then estimated growth of the family according to birth rates. I estimated that this couple has around 25,000 descendants today (they had very large families in the first four generations - around ten children each). Also, even with the modest birth rate of today, each generation adds another 50,000 descendants. This is around 1,500 new descendants each year. Of course, these are not the Olliff surname. Since an average family history book contains 7,500 descendants - it would take a new book every five years to keep up !

    http://www.rcasey.net/acrobat/oll0907n.pdf#Page=472
    Last edited by RobertCasey; 04-02-2017 at 04:50 PM.

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    Quote Originally Posted by A.Morup View Post
    Please be aware, that I am not 100% sure that my calculations are right!
    And even if they are, remember that I look downstream from myself - the calculations are the odds that my personal Y-DNA will survive.

    When it comes to other living people with the same Y-DNA as me, that is a different story. I have made a special "Y-DNA tree" for myself. It starts with my most distant known male ancestor (born ~1655) and then follows only male lines downstream. That was when it occured to me how fast male lines have died out in my line. Not necessarily in the first generation, but then after one or two more...

    And for those of you, who have taken BigY and are lucky enough to have one or two close BigY matches, have a look at this project of mine that mixes the fields of male line genealogy and "private" SNP testing: http://www.anthrogenica.com/showthre...te-SNP-project

    When it comes to Y-DNA it all comes up to how you see the world:
    - Looking backwards, every human has a direct male line
    - Looking forewards, it is very unsure whether you will have a male line or not

    Kind regards
    Anders
    Yes, I understood you to be speaking of your own male line. However, my point was that if you're only focused on your Y chromosome, for all intents and purposes there probably is no meaningful difference between your Y chromosome and that of your patrilineal relatives.

    So while I personally have no sons, two of my brothers have sons and one of the sons has a son. I would guess that my grandnephew's Y chromosome is nearly as close a match to mine as my own son would be. This is not only true for my nephew, but also likely for my patrilineal 1st and 2nd cousins, and their direct male descendants.

    That also means I don't need to feel "burdened" by any failure to pass on the family Y. Besides, I passed on my X chromosome, which is literally "a bigger deal". (In that the X chromosome has considerably more DNA than the Y chromosome.)

    50% of my daughter's DNA is from me, and actually I passed on a little more than 50% of my DNA to her (because of that X/Y size differential). If I had a son, he would have inherited more of his DNA from his mother than from me ... not that it truly matters. That's just the way it works.
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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    Quote Originally Posted by RobertCasey View Post
    Having only two children is a pretty recent change in the number of children per couple. During the 1700s and 1800s, the families were much larger. However, your math will be more representative of many generations to come. There are some exceptions even today where birth rates are much higher: 1) LDS and Catholics are encouraged to have large families (although Catholic birth rates are declining from the past); 2) immigrant families from Latin America to the US continue to have large families (similar to my recent ancestors and the Catholic influence); 3) African Americans used to have very large recent families but their birth rates are greatly declining as well.

    Also, there have been periods of very high mortality rates in specific areas. Ireland has many of these periods in the recent past: 1) potato famines of the mid 1800s; 2) the great crop failures of the 1740s (my Caseys came to the US then); 3) invasions of the Vikings, Danes and English; 4) intense warfare from many regional kings to all of Ireland under the Dal Cais (L226) and O'Neill (M222) at the expense of their neighbors; 5) the great plague; 6) and during the last great Ice Age the population of Ireland went to zero since it was under a couple of miles of ice.

    So, birth rates and death rates varied significantly which is a major factor.
    I'm glad you mention both birth rate and death rate. It hasn't always been about how many children a couple had, but how many survived into adulthood. For example, my paternal grandfather father was one of seven or eight children. Only he and his eldest sister survived long enough to have families of their own -- but it wasn't that their mother only bore two children to begin with.

    Quote Originally Posted by RobertCasey View Post
    There was an article some time ago that stated that over 90 % of all our male ancestors have no living male descendant today.
    http://www.rcasey.net/acrobat/oll0907n.pdf#Page=472
    I suspect that isn't quite what they mean, even if that's how they put it. I presume that what's meant is no direct male descendant -- or no living descendants in an all-male line.

    My brothers and I are male descendants of our mother's father, after all. But since we're his daughter's sons rather than his son's sons, we didn't inherit his Y chromosome. However, my eldest brother inherited his X chromosome entirely from this grandfather, with no input from our grandmother. I nearly did, but about 30 cM around the centromere of my X chromosome came from my grandmother.

    Ironically, even though my grandfather does have a male-line descendant in the form of my 1st cousin Al, it seems very likely that my grandfather was not the biological son of the man who raised him. So while my grandfather -- and Al -- inherited the Y chromosome of my grandfather's father, that man wasn't the man he was claimed to be, anyway.

    (However, in this case it seems that my grandfather was not only the product of an NPE, but of an NME as well. Neither of his parents seems to have been who they were supposed to be!)
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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