Posts tagged ‘chromosomes’
DNA technology is advancing so rapidly that it is difficult to keep abreast of the advances and possibilities. Moreover rapidly falling prices make genetic testing more affordable and so more accessible. Here are some current options:
Test 1: Y-chromosome tests, for males to test DNA inherited from their father’s fathers
It is now possible for under US$200 for males to test the DNA they have inherited from their father’s father’s fathers, with sufficient accuracy to determine whether two men likely share a common ancestor ‘within a genealogical timeframe’ and how many generations ago that common ancestor probably lived.
I have used this test to discern whether two families with the same surname were actually related to each other, in situations where I have not yet found documentary proof. I have also used this particular DNA test to check (and finally refute) a theory about who might have been the biological father of an adopted male. It was necessary to find a living male descendant (down an all-male line) from the adopted male and also to find a living male descendant (down an all-male line) from the hypothesised birth father, and then compare the DNA that each inherited from their father’s fathers.
DNA is not related to surnames and so I am not restricted to testing two men with the same surname – the test is valid for any two men who might share a common male ancestor. However when I order this test, if I choose to use a commercial testing company like Family Tree DNA – which has a huge (and growing) database – I might find in their database a match with some living descendant who shares a common ancestor that I did not know about. This is especially useful for adoptees.
The above DNA test is only available to males (as only males have a Y-chromosome). Females like me need to ask a near male relative to be tested. I have asked my father and also my mother’s brother to be tested – this opens up for examination my nearest male lines.
Test 2: Mitochondrial tests, for anyone to test DNA inherited from their mother’s mothers
Useful DNA tests are no longer limited to males. We all have a different type of DNA (called mitochondria) that we inherit from our mother’s mother’s mothers. Mitochondria mutates so slowly that formerly the only conclusions we could draw from our maternal line was about ancient ancestors and their migratory patterns.
However that is no longer true. The company Family Tree DNA offers full sequence tests of all our mitochondria (DNA that is inherited from our mothers) that allow us to identify people who share an ancestor through our mother’s mother’s mothers, within about 200 years. [Thank you Bill Hurst for pointing out that while 23andMe also tests the ‘coding region’ of our mitochondria, they do not test or give results for all 16,571 locations, so theirs is not in fact a full sequence test.]
When the above matrilineal full sequence tests first became available, they cost close to $1,000. That price has dropped now to under US$300 (sometimes under $200).
Test 3: Autosomal tests, to test the DNA inherited half from each of our parents
We are not restricted to testing only the DNA of our father’s fathers or our mother’s mothers. Since 2010 it is possible to test the remaining nuclear DNA (that is, not the sex chromosomes). This DNA is called autosomal. Family Tree DNA calls their autosomal test Family Finder, while 23andMe calls a similar test Relative Finder. (Again these tests are under US$300 and sometimes under $200.)
These particular tests can check the DNA of our ancestors regardless of gender, because we inherit about half our autosomal DNA from each of our parents (and via them, from their ancestors) and this DNA can also be compared with the DNA of others. However as we inherit about one quarter of our DNA from each of our grandparents (and so about one eighth from each of our great grandparents) – eventually the inherited material from one particular ancestor becomes so small as to be difficult to identify definitively. Consequently, when comparing this autosomal DNA with someone else, our best conclusions are when the common ancestor lived no more than about 6 generations ago.
Use the tests in conjunction
While the above tests examine separate DNA, the tests can be used in conjunction. When looking at the summary of DNA results for people that 23andMe identified as likely to be my 3rd to 5th cousins (identified via the Relative Finder – or autosomal test), I noticed that one of the matches also seemed to have very similar Y-chromosome (father’s fathers) DNA to my mother’s brother. I sent an email and by swapping names of grandparents and their parents, we soon identified that this person was the son of a 3rd cousin to me (and so indeed within the range of 3rd to 5th cousins).
It is not necessary to understand how a car works in order to drive it, but it is necessary to know the functions of driving. In the same way it is unnecessary to understand much about the science of DNA in order to use it as a tool – but it is necessary to understand what sorts of questions can be answered by the different DNA tests so you know how to apply them as tools to aid your family history research.
This field is changing quickly
Because genetic tests available to the public are changing frequently (and certainly the prices are) readers need to beware of relying on conclusions written years ago or by someone who has not ‘kept up’ with tests currently available. This blog post is partly in response to an article I read this week entitled ‘The DNA dilemma’ – I do not agree with many of the conclusions in that piece.
It is no longer true to say that the only available information to be derived from maternal DNA (or mitochondria) is about ancient migrations of peoples – recent relatives can now be found by a full sequencing of the mitochondria (test available from Family Tree DNA for under $300).
It is no longer true that autosomal DNA can only make generalised indicators of race origins. (Autosomal DNA is sometimes referred to as ‘nuclear DNA’ but that is incorrect because the sex chromosomes are also inside the cell nucleus and the autosomes are the other pairs of chromosomes that are not the sex chromosomes.) Nor is it necessary to ‘test each generation in turn’. Autosomal DNA can identify that two people shared common ancestors within 6 generations (and possibly beyond, but it is less accurate beyond 6 generations). Many genealogists will not know all of their ancestors back even 6 generations, and so this DNA test can predict likely distant cousins who may not have been found by a paper trail.
There are differences between the DNA tests used in forensic law enforcement compared to commercial tests. Without going into too much scientific detail, legal forensics examine repeating groups of DNA at certain points on the autosomes whereas commercial autosomal tests examine the autosomal SNPs (something like ‘typo’ mutations). The tests are entirely different. Be wary about confusing the markers referred to in tests of the Y-chromosome (the DNA inherited father-to-son) – which are entirely different to the markers of autosomal DNA examined by forensic law enforcement agents.
Some people have suggested that male DNA studies are only relevant between males who share surnames. That is not true. There are many examples where family trees show a son with a different surname to his father – whether the name was changed by deed poll, by adoption, by remarriage of the mother – or for many other reasons. It is not the same surname that defines two people as father and son. Likewise DNA tests do not take surnames into account, so the test result is just as accurate whether two men share a surname or not.
In my opinion, the most recent DNA tests available to genealogists offer precise information which can supplement traditional genealogical methods. Family trees are still needed to identify ancestors and draw conclusions, however DNA tests can supplement other genealogical research, filling in gaps left by paper trails. With such tools we can test our conclusions and assumptions in constructed family trees as DNA can confirm or disprove reputed relationships. As databases grow, commercial DNA tests are more likely to help us find relatives that we might not have found by ‘traditional methods’.
I started down the DNA learning path several years ago. My Dad’s father was adopted, & when I eventually found his birth certificate it contained no information about his father. An unusual middle name and circumstantial evidence suggested someone, but with no documentary evidence, DNA seemed a way to test my theory.
I found a grandson of this possible ancestor – son of a son, so a good candidate for y-chromosome DNA comparison with my father. I asked – if I paid for it, would he be willing to have his DNA tested to compare with my father’s DNA? He said yes, but unfortunately the test proved that he and my father were not related. (DNA is often better at disproving rather than proving relationships.)
I used the company Family Tree DNA, which has the largest database for testing and comparison, and now that I am registered, I am advised when others match my Dad’s DNA. I hope that one day I will find someone with the right DNA,who had an ancestor in the right place and at the right time.
Some time later, I had the opportunity to speak to Megan Smolenyak about my problem & confirm my method. I asked Megan for her advice about which company should I use to test my Mum’s DNA.
Females don’t have y-chromosomes so cannot have the y-DNA tests done. However humans have other DNA outside the cell nucleus, called mitochondrial DNA (mtDNA). Mothers pass mtDNA to all their children, but only their daughters pass it on. I wanted my Mum’s DNA to be tested now and also stored for the future, for as-yet-undeveloped tests. Forensic scientists use mitochondrial DNA now, but for genealogists mtDNA is mostly only used for deep ancestry testing, not for finding ‘recent’ ancestors (those in a genealogical timeframe).
Megan suggested that I have my mother’s DNA tested with the company 23andMe, as they were developing new tests and could offer more information about female ancestors. 23andMe tests give information about genetic health issues, in addition to genealogical ancestry matching – so I took that advice.
These 2 companies that I had used (23andMe & FamilyTreeDNA) offer very different information in their test results. Results from the FamilyTreeDNA tests are tables of numbers, indicating the DNA at specific genetic marker points. There is also a YSearch database for comparing results, and even people who have had their DNA tested with other companies can search this freely – you manually enter the numbers (alleles) at various marker locations and see if the results match anyone in the YSearch database.
The results from 23andMe gave information about genetic health risks and tendencies and general DNA groupings – it required a bit more delving to actually find the numbers that correspond to the (mitochondrial) DNA markers.
Around a year ago, both these companies announced new tests involving autosomal DNA. 23andMe call this ‘Relative Finder’ – FamilyTreeDNA call it ‘Family Finder’. Humans have 23 pairs of chromosomes in every cell nucleus – 22 pairs of autosomes and also another pair, the ‘sex chromosomes’ (XX for females, XY for males). The autosomes contain bits of DNA inherited from all your ancestors, not just from all-male or all-female lines. You share larger pieces of DNA in common with close relatives, and smaller bits of autosomal DNA with relatives less closely related.
Both males and females have this autosomal DNA, so now you can find relationships with anyone sharing any common ancestor, not just the all-paternal or all-maternal lines. This new autosomal DNA test has thrown up some new possibilities and new candidates in the search for my father’s father’s heritage. (We already have found a close relative with interesting possibilities.)
However, back to the initial subject. The company 23andMe is offering a special price for the next few days, and some Facebook friends decided to take advantage of it. I agonised whether I should join them, given that I already have tested my father’s DNA as well as my mother’s mitochondrial DNA.
In terms of autosomal DNA, although the test is new, I suspect that the company FamilyTreeDNA is likely to have a bigger database for comparisons. (For me the main value of DNA tests is looking to match with others, and so larger databases are better.)
But 23andMe gives other information – about genetic related diseases – in addition to the study of ancestry. I have decided that both companies’ tests are of interest to me. So now I too have taken advantage of the current special price, and will get my own DNA tested.
Of course there are many other testing companies, and websites with information about DNA. I give talks about ‘DNA for Genealogists’ (my handout can be found on my website). The handout contains information about various testing companies and their information pages, as well as other sites with DNA tutorials, mailing lists and even a DNA Wiki.
For now though, I have joined the ranks of those waiting for a test tube to be posted to me, so I can take the next step in this DNA journey.