Suppose a sperm sample at a crime scene is consistent with a person and any “patrilineal male relative.” How far back does that mean? 1 generation? 2? 50?
Thanks.
As I understand, they’ve used this to identify direct male descendants of Thomas Jefferson (both his legitimate children and the children of his slave mistress; although this leads to the dispute “how do we know that Sally Hemmings’ children were not from Jefferson’s brother or cousin who apparently were also on the plantation?” So children born in the 1790’s and their father through people alive today. Allowing about 25 years per generation, 1790 to 1990 is 8 generations. Not sure when the test was done.
Then, of course, there’s no guarantee that the patrilineal sequence is as advertised. The polite term is “pedigree error” when the father is not who the family thinks it is. If somewhere down the chain one mother was unfaithful (with someone also not a direct male descendant), it is difficult to prove. This is where it helps to have multiple subjects to test.
Realistically, probably only about 4-5 generations.
Because a generation is typically 20 years, so 4 back would be a guy about 80-some years old.
Most Great-Grandpas in their 80s aren’t gonna be leaving many sperm samples around, crime scene or anywhere.
No, an 80 year old guy wouldn’t, but what about his great-grandchildren, the somewhat distant cousins of the initial suspect?
I guess my question is one of degree. If we trace the Y chromosome back to the earliest common ancestor, then all males in the world would have the same Y chromosome. However, I understand that after many generations, mutations occur.
But it seems like back to Jefferson’s day (200 years) is good enough, so how far back would that continue? And if it goes back a minimum of 200 years, it seems than a DNA sample as discussed in the OP could encompass thousands of people at least.
It’s not a pure matte of match or no match. Given a partial match, it’s possible to estimate how far back the common ancestor was. This is how we know that a major chunk of Eurasia is descended in the male line from Genghis Khan, and how we can verify that most of the Cohens in the world, who are claimed to be male-line descendants of Aaron, apparently actually are.
Okay, here is the quote: “[Mr. X] cannot be excluded as the source of the male DNA…in addition, all patrilinerally related male relatives cannot be excluded as being potential donors to the male DNA from the above sample barring mutational events.”
Is there a typical meaning for that which does not involve “all male descendants of Genghis Khan” or do I need to delve into the science behind it?
Is there a difference between “source” and “potential donor”?
I mean, surely a crime lab isn’t going to be misleading by using such seemingly specific language if what they really mean is “this DNA could have come from any white dude in the entire world.”
Tony Randall procreated at his late 70s, it is the woman that loses the ability to procreate without serious medical help [my sister in law had kids at 50 via IVF, insane woman that she is. I can’t imagine running after toddlers in my 50s … ]
In most cases (i.e., those not involving the most successful conqueror in history, or a religious naming convention from a religion that really cares about absolute paternity), uncertainty in paternity will become the dominant uncertainty much more quickly than the rate of mutation-induced variation, so the CSI lab doesn’t need to qualify their assessment any further.
Perhaps I am misunderstanding or have a misconception. I am not worried about great-grandma cheating on great-grandpa and my genealogy being wrong.
What I am asking is that if we know that most Eurasian males can trace their patrilineal line to Genghis Khan, then what does the CSI’s statement mean? Again, surely it isn’t couching a seemingly specific statement in a conclusion that broad. IOW, Mr. X should have nothing to fear from that conclusion because, although he cannot be excluded, it is likely that most if not all other other males in the community (indeed descended from two full continents) can similarly not be excluded. The results might as well not even be there.
But again, I would be surprised if the lab engaged in such trickery. So if it is not engaging in trickery, what would be the typical limits of a patrilineal line in such a statement?
First of all, it’s not “most” of Eurasia descended from Genghis. I said “a major chunk”. Looking it up, it’s about 8%.
Those men all have very similar Y chromosomes, but they’re not identical. Based on the known rate of mutations, you can take that degree of similarity and use it to determine roughly when the common ancestor lived, which is part of how they know that it came from Genghis. But based on those differences, a crime lab would have no great difficulty in distinguishing between those men.
The point, though, is that if they have a match for one suspect, it could very well be his brother, or father, or son, or paternal uncle, or cousin, or so on. It could also be, say, his fifth cousin… but that’s not very relevant for a criminal investigation, because by the time you get that far out, you probably don’t even know who the fifth cousins are: Not just because of nonpaternity events (which don’t necessarily involve cheating), but because it’s likely that nobody in the known family has made a hobby of genealogy. And by the time you get to where the mutation rate is enough to make a difference, it’s hopeless to know the full family tree. In other words, genetic science is not the limiting factor in finding the suspect list.
I’m in my sixties and I’m doing it.
It’s not easy – they’re fast little fuckers.
The number / frequency of illegitimate children doesn’t affect the answer, because the question isn’t about the ‘name’ of the children.
If you have 1 biological brother, and your father had 1 biological brother who himself had 2 sons, (that’s 4)
And your grandfather had 1 biological brother with 2 biological sons each with 2 (that’s 8)
And your great-great grandfather (3 rd generation), that makes 16 men at about your age all in straight patrilineal descent.
How far back can you trace the biological identity? Nonpaternity events are irrelevant.
This is my question and I simply must not be asking it articulately. Say that CSI report identified me as a “cannot be excluded” but also said that it could be from my patrilineal male relatives. How worried should I be?
Have they narrowed it down to me and possibly a brother or cousin? Or have they captured a substantial minority of the entire white population of the area?
Wouldn’t it be more that, based on history they assume it’s Genghis, but based on DNA all they know is it was some guy alive at around Genghis’ time?
I assume there are some families in Mongolia who can assert with confidence they are descended from Genghis. However, yes, they may also be descended from his father, grandfather, etc. by a different line. The divergence (mutation) of the Y can be approximately dated to say “all these men all across Eurasia have a common male ancestor about 1,000 to 1,500 years ago”
“Pedigree errors” are relevant to tell you that if you are comparing A and B, they will not have the same Y -it may be radically different - even though genealogy claims they are patrilineally related - for example, some of Jefferson’s slave-side “descendants” apparently don’t match. (Some do) This implies in some place, the family tree is wrong. You test based on family trees, then determine if the genetics are correct. (It’s not always cheating. Sometimes adoptions or children by previous relationship are not widely known, or forgotten generations later.)
For forensic purposes, the police would need more than the Y-chromosome to charge, let alone convict someone - particularly because of what you’re asking: hundreds of people could be a close match for that Y. Besides - most DNA evidence doesn’t come with the Y chromosome pre-separated.
The case of Christine Jessop is instructive. Guy-Paul Morin was charged, based on basically almost nothing except police gut feelings. Midway through his third trial, DNA technology became possible, and he was cleared. Decades later, the actual murder was already dead - but by using DNA and relative matches, they fingered the real murderer. This happened because they could match him to two completely unrelated families using relative DNA matches. Tracing the connections between the two families, he was the only one who would have DNA from both (and the age and opportunity to commit the crime).
(Fun fact to contemplate - I look at assorted family trees I know. To sustain our population, a parent should on average have 2 children, 4 grandchildren, 8 great grandchildren, etc. Of the families I know - my grandfather had 3 children who have had 8 grandchildren (4 childless) who have had 6 ggc. My wife on one side, grandma has 3 children, 3 gc, 4 ggc. On the other side, grandma has 4 children, 3gc, 4ggc; Our population simply isn’t even keeping up by this generation and the next- if it weren’t for immigration, our population might be shrinking already.)
If your question is “How many people in this city (or county or state or continent or whatever) would be expected to be consistent with these test results”, then you would need to ask that question directly of the people who performed the test, as it would depend on information we don’t know, like how detailed the test was, how good the quality of the sample used was, and how common that particular lineage is in that particular area (which might approximately correspond to how common that surname is, although nonpaternity events are likely more common among the population typically suspected of crimes). You could also try asking the suspect if he personally knows of any male-line relatives.
The other issue is population mobility. I suspect the range of distinct patrilineal results is dependent on population mixing. In some quiet hill town in Sicily or one of the Polynesian islands, I’m guessing you will find fewer distinct Y’s than in say, a town in suburban USA or urban Paris.