The Study of Racialism

How long does it take for Y-chromosomes and mitochondrial dna to mutate? For how long do they remain unchanged?

Also, how can dna testing (through Y-chromosome and mtdna) trace Western Blacks to an African ethnic group if those groups are relatively young? What distinguishes them genetically from the groups they may descend from?

The first question is more important. Thank you

I don't think the mutation rate is a settled issue. The mutation rate depends on the area of the chromasome (or mitochondria) that is being tested. The greater the area tested means each mutation is less significant over all. If you google the mutation rate, you'll see what I mean. ( I know this isn't a great explanation, but I though copying and pasting someone elses debate on the issue seemed, well, over the top.)

All the mtDNA and YDNA tests can show is that two people have a common ancestor along the maternal or paternal line, respectively, within a rough time frame (i.e. 800-2000 years ago) or approximately ___ generations. What distinguishes one individual from another, with respect to their entire genome, when two individuals share an identical portion of mtDNA or YDNA will vary enourmously from case to case. The tests show the common ancestor, nothing more. So, what the tests can show is that a american (and I use the term in the wider, hemisphere wide definition) has a common ancestor along the paternal or maternal line with someone who is now a member of the ___________ tribe in Africa. Doesn't necessarily mean that the ancestor was a member of that tribe, or even that they lived in the same part of Africa. People move around, and reproduce in different places that where they were born. But it shows some connection.

Human mtDNA mutates at about 2 percent per million years. In the past 200 millennia, the mtDNA lineage from which which all living humans descend has mutated into about 150 lineages. Some existing lineages (L1a, L1d, L1f, L1k) are very ancient, having remained unchanged for 150 millennia. Other existing lineages (M7b1) are much more recent, having arisen just 15 millennia ago. On average, mtDNA has split into different existing lineages roughly once every 22 millennia. (The number of original mutations is higher because many lineages have become extinct.) Y DNA is less well-studied, but as far as anyone can tell, the mutation rate is about the same. You can download and print a fullscale family tree of existing mtDNA lineages here, and you can download a similar family tree of existing YDNA lineages here.


Neither mtDNA nor YDNA can identify "ethnic groups." "Ethnicity" is a modern concept tied to political affiliation or allegiance. Matrilineal and patrilineal lineages can trace the migration of genetic populations, but such traits cannot unambiguously identify tribes, nations, states, nor any other political level of organization.

Autosomal DNA (in contrast to mtDNA or YDNA) does carry markers that correlate with major world regions, and so can be used to compute what fraction of your genome comes from, say, Asia or Africa, but subdividing autosomal DNA any finer than that is a matter of probabilities. For example, a particular marker might be found in 5 percent of Senegalese, 3 percent of Kenyans, 4 percent of Somalis, and 2 percent of Berbers.

Judging by your previous posts to this forum, I wonder if you are perhaps seeking a way of delineating socio-political alliances among today's Africans. If so, I suggest that the "International Stories" forum might be a more suitable venue.

From what I've seen individuals researching their genetic history do not receive the added information about sharing a common ancestor with respect to a particular time frame. This explains how a black male with West African heritage is told his YDNA or paternal line descends to central Europe.


I see, so even though a tribe or villiage may have others with a number of similar markers to an American taking such tests, those markers do not mark that geographic location.

It seems that the best use of mtDNA and Y in molecular anthropology is to determine that admixture occurred. For example, if a European has a mtDNA "L" sequence, we know that he has a sub-Saharan African somewhere in his maternal lineage. If he has a Y "A" sequence, we know he has a sub-Saharan African somewhere in his paternal lineage. But we do no know for certain when this admixture took place, nor can we determine the percentage of an individual's admixture from his mtDNA or Y-chromosome. If the country has a slave-trading past, like Britain, Holland, Portugal, etc., or if the country is situated in the Mediterranean (especially, but not only, if it was occupied or raided by Saracens, Moors, etc., who had sub-Saharans in their ranks and who had sub-Saharan admixture themselves), then we can assume that the sub-Saharan mtDNA or Y sequence came from this time, and we'd probably be right. But we still can't be certain. All we can be certain of is that admixture occurred.

If you don't have access to a printer take a browse through National Geographic's colourfully illustrative Genographic Atlas.

The Map of Us All describes this Genographic Project spearheaded by population geneticist, Spencer Wells.


Interesting. What scientific validity do you give to services like this one:

http://www.rootsforreal.com/service_en.php

and how might it compare to those based in Autosomal DNA?

Thanks William. It makes clear how science is not yet up to putting these questions beyond doubt. Would be great to identify and hold in isolation the genographic map as it stood around AD 700, me thinks.

I've looked at that, and it is very interesting. I also read the short article in the magazine itself a few months back.




I am a bit skeptical of the idea that the area of one's mtDNA's or Y-chromosome's geographic origins can be determined through finding a match, other than perhaps to give a broad geographic location, like "Eastern sub-Saharan Africa," or something similar, based on haplogroup.

Also, one's mtDNA and Y-chromosome represent a very small part of one's genetic composition. Ten generations ago, one had over 1,000 ancestors. mtDNA and Y testing would tell us only about two of them. Autosomal testing would tell an individual much more about his genetic compostion.

That is the problem in a nutshell. I have deep respect for genealogists, especially since many attend my presentations. But, when you come down to it, genealogy resembles history-writing. It is a search for interesting stories in the past. Given that you had 1000 ancestors alive in the year 1800, how can you trace those of human interest?

MtDNA and YDNA let you focus on two specific individuals. Your patrilineal and matrilineal ancestors were real people, they lived, they had stories. The thing is that each of them contributed only 1/1000th of your genome (virtually nil).

On the other hand, your autosomal DNA is truly you (at least, genetically speaking). If your autosomal DNA is 20% sub-Saharan African, 30% percent European, 30% South Asian, and 20% Native American, then that is what you are. To a first approximation that is how your 1000 ancestors in the year 1800 sort themselves out. But there is no human interest story in autosomal DNA because there are no individuals, just numbers.

In my view, people have the right to seek interesting stories wherever they wish. "Scientific validity" has nothing to do with it.

Hi Frank,

I believe those percentages are just approximations to what individuals are. Actually, what the tests detect are markers that are just certain patterns in an ocean of DNA code. If the result say 30% South Asian it is just telling in the result a 30% of South East Asian markers were found. They don't tell that a person has a 30% of South East Asian DNA at all (if such a thing exists). And they are not telling that a person has a 30% of South East Asian ancestry either (people in the family tree).

As we know, genetics is a matter of chances. Is a game of probablilities. And chances are what the test show is close to the truth, but there is not certainty of that. So, that's why a genetic test can give a different result that other.

Finally, my point is, genetic tests give clues but are not conclusive about the percentage of ancestry an individual has. As an example, a person could mark 0% native american and still have ancestors and genetics of Native americans, including the right phenotype.

Don't you agree, Frank?

Regards,

Omar Vega

Absolutely. It is all a matter of probabilities. Somewhere in this forum I posted the formula for the 95% confidence interval. In short, the more markers you test, and the more reliable they are, the narrower the confidence interval. And so, when you say that someone has 20% south Asian DNA, you are really saying (depending on the two factors above) that you are 95% certain that the person as between, say, 15% and 25% south Asian DNA. The second point you made, that a person's genome might not match his historical ancestry is also valid. It is possible that some group of actual past ancestors may be over- or under-represented in a person's genome by sheer luck. The likelihood of this would also fall within the same confidence interval.

A valid complaint I was given at Hall of Maat
http://www.hallofmaat.com/read.php?1,37 ... msg-375372

Yes, Gisele's arguments are valid. In fact, the entire mtDNA haplogroup classification is Eurocentric, as Frank and I have discussed in the past. Sub-Saharans were all classed with L's (except for sub-Saharan East Africans lineages classed as M1) despite their being the oldest, and hence, most genetically diverse, people on the planet. Seems a little silly. As Frank said, that makes about as much sense as dividing all living things into 14 groups, with 13 of them being different breeds of dogs, and the last one containing everything else.

An obvious touch of exaggeration, from Horvat, in the linked forum. Mention is made of Siberian haplogroups, while "Figure 5 (page 11) [eprints.ouls.ox.ac.uk]", details the southern OOA coastal route.

One odd feature on the Genographic Map is the dot around the location of Cairo with the label [Neanderthal (Asia)] containing text about the skull found in Germany's Neander valley in 1856.

http://www.hallofmaat.com/read.php?1,37 ... msg-375388

That was probably a glitch. LOL

I had a fun time with an Afrocentric who treied claiming Europeans were neandertals with obvious ignorance that there were neandertals in n africa as well.

It still gives an overall depiction of the spread of haplogroups through Eurasia, including Siberia.

Most people aren't aware that no Neandertal DNA has been found in Europeans. Supposed crosses were found by anthropologists, like the one found in Portugal a few years ago. But they apparently were dead-ends.

Hi,

It looks like modern humans see Neandertals as if they were from another group of mammals. Actually, Neandertals were humans like us. Perhaps they were not as intelligent but certainly they were humans. They not only knew how to make fire, cloths and weapons, but also manufactured arts and buried their deaths.

When we speak about neardentals we are not talking about australopitecus or other ancient creatures; which are really allien to us and closer to chimps. With Neardentals we are talking about a close relative of us.

I wonder if they passed away just because natural forces, or if their extinction was one of the first genocides commited by mankind. I am afraid I know what happened already.

The sad point is that the last place where Neardentals existed it was Spain, near Gibraltar.

Regards,

Omar Vega

Yeah, I know, but most people are stumped on genetics and go by geography for their assumptions. So I gave them something to chew on with their assumptiveness.

Oh, I know that. I'm not suggesting they're not related to us; only that none of their DNA has been found in modern Europeans. I would find it fascinating if such DNA were found. It would cause us to re-write history.



I wouldn't jump to conclusions and say that there was a genocide involved in their disappearance. It could be that since Cro-Magnon man is (regarded as) more advanced and skilled, perhaps they simply out-competed the Neandertals for food. Then again, the Neandertals thrived for at least 150,000 years in terrible ice-age conditions. Who knows...but I don't think I'd chalk it up to genocide.