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Ancestry DNA Question

Ancestry DNA Question

Posted: 10 Oct 2013 3:45AM GMT
Classification: Query
Maybe someone can help me here. I have been long interested in getting my personal genome tested and the Ancestry autosomal kit seems to be the ticket... however:

For the sheer fact that these types of tests involve so many place makers in one's own genetic makeup means little to me, as I have studied what happens to one's DNA in advanced college courses. The upshot of things is that one's parent's contributing DNA readily swap base pairs among themselves as cells divide. In other words, you become a truly complete mixture of your parent's DNA. Except... if you are a male.

Because of the mismatching XY chromosomes at DNA pair 23, crossover does not readily happen, if at all. That is why the 40 Y male chromosome is useful for tracing a male's immediate ancestry. The other 22 chromosomes that we each carry becomes very analogous to mixing a paint bucket with dyes to result in a very specific color and explains why one's siblings do not look like a twin, but still resemble each other... as you and your siblings are made of the same DNA "ingredients" contributed by each of your biological parents.

The question being posed here, is that does Ancestry autosomal DNA testing also include the 40 base pairs being tested in Y (male only) DNA tests? I cannot get an answer to this basic question. The premise is very true that only males can pass down the line the "Y" gene. Otherwise, matched "XX" chromosomes readily mix - just like dyes being put into a paint bucket and shook.

Does anyone have insight into this concerning Ancestry's test? They are very strangely silent and have the male specific (for us living guys... sorry girls, nature defines you do not get this research advantage) included would be extremely useful and make their offering a true bargain! (Girls, you can leverage this too by getting a brother to do the mouth swab for testing, instead of doing this yourself).

Thanks for any comments here. I am very interested, but do not want to spend the $ if all I am going to get is generalities either.

Re: Ancestry DNA Question

Posted: 10 Oct 2013 9:59AM GMT
Classification: Query
"...I have studied what happens to one's DNA in advanced college courses."

My DNA never got to take "advanced college courses" so nothing has happened to it. :)~

Joking aside, if I'm understanding your question correctly then No, Ancestry's Autosomal DNA (atDNA) test does not also include a Y DNA (yDNA) test.

If you're interested in yDNA testing I'd suggest going with FTDNA. While Ancestry is more or less leading the charge with regard to atDNA testing it's yDNA participation is weak at best.

Re: Ancestry DNA Question

Posted: 10 Oct 2013 1:07PM GMT
Classification: Query
I gather you refer to Y STR tests (Short Tandem Repeat), which measure the length of a fragment of DNA, not specific base pairs. The autosomal DNA test uses an entirely method, which does look at specific base pairs. If you are interested only in your straight paternal line, the Y STRs are a very good approach, and FTDNA (as mentioned above) is considered the best company for that type of test. It can measure as many as 111 STRs.

However, autosomal DNA doesn't blend like paint. It's more like mixing red and yellow jelly beans than red and yellow Jello. The DNA is chopped up with each generation, but the pieces retain their identity and can sometimes be traced to a specific ancestor (with luck and hard work). If you're hoping to find a match who knows more about your brick wall than you do, the autosomal DNA might identify such a cousin from any line of descent. These animations show how that works:

http://www.smgf.org/pages/animations.jspx

Re: Ancestry DNA Question

Posted: 11 Oct 2013 5:16PM GMT
Classification: Query
Read about how recombination really works.

Each chromosome is an extremely large molecule, but during meiosis undergoes relatively few crossovers.

This means large segments of DNA are shared between relatives. It is this fact upon which AncestryDNA matching depends.

Re: Ancestry DNA Question

Posted: 11 Oct 2013 6:45PM GMT
Classification: Query
Agreed that during meiosis, crossover is not as common, as the paired chromosomal diploids are eventually sliced into four chromosomal haploids through a two step splitting process. However, by the time the teste cell is programmed to undergo meiosis, crossover has occurred many times. This occurs with cell multiplication from within the developing embryo and that eventually leads to specialization into organs, such as the testes.

You are always 50:50 your parents' DNA, but the percentage you are of any given grandparent's DNA can greatly vary due to this fact. That is why siblings often favor one of their parental lines and the other sibling more resemble the other parents'.

Re: Ancestry DNA Question

Posted: 12 Oct 2013 5:34AM GMT
Classification: Query
Before you test, I suggest you read these four articles that will explain what you can and cannot do by the genetic genealogy guru, CeCe Moore. It will also help you understand genetic genealogy terminology.

Y-DNA Testing for Genealogy
Very Basic Intro to Y-DNA Testing
http://www.geni.com/blog/dna-testing-for-genealogy-getting-s...

Mitochrondrial DNA Testing for Genelaogy
Very Basic Intro to mtDNA Testing
http://www.geni.com/blog/dna-testing-for-genealogy-getting-s...

Autosomal DNA Testing for Genealogy
Very Basic intro to atDNA testing
http://www.geni.com/blog/dna-testing-for-genealogy-getting-s...

Percentage Breakdowns: DNA Testing for Ancestral Origins
Intro to "Ethnic Percentages" by DNA
http://www.geni.com/blog/dna-testing-for-genealogy-getting-s...#

And just for the record, once a female reaches 12 she is a young woman. We are not girls.

Re: Ancestry DNA Question

Posted: 12 Oct 2013 7:01PM GMT
Classification: Query
Edited: 12 Oct 2013 7:04PM GMT
Thanks for the links, I will check them out. As far as the age when a "girl" becomes a "woman," that does not biologically begin until menses commences and the maturation process does not fully settle out for several years afterwards. There is no set age for that, as the commencement of biological maturation varies greatly among individuals. The law is very very clear about defining an age of maturation for overall very good reasons that has more to do with societal norms though.

Re: Ancestry DNA Question

Posted: 12 Oct 2013 8:49PM GMT
Classification: Query
Edited: 12 Oct 2013 8:55PM GMT
Hi I checked out these links and particularly the Autosomal DNA Testing one as that is where my initial inquiry lay. That particular article is misleading through it's over simplification of how the average contribution from grandparents (and further back) any one given individual may actually hold within themselves as to actual genetic makeup. The really big factor in this is "crossover" or, more accurately put, natural DNA recombination that occurs when a cell spits into two functional selves. We all start off as a single cell (fertilized egg in the mother's body). For that fact alone, you will always be 50:50 your parent's contribution.

The real wildcard lay with what part of your parent's genetic makeup got saved to make you. Only half of their own specific genetic make up got saved to combine into viable cell which developed into you... with the rest discarded or not used (depending upon gender). Crossover occurs each and every time a cell divides during 'normal' cell division and is completely random in nature. By the time the a cell is destined to become either an egg or sperm, this has happened countless times... and only one of their own progeny goes on to result in a new human being. It is entirely random which specific bits of paired DNA exchange place and which combining sexual cells actually gets used to result in the baby. (The rest get's thrown out... a female's actual period is the result of discarding a fully ready sexual cell that 'could have become a person'). The same for any of a guy's unused sperm that does not goes on to do the same.

Of any given sample of a male's sperm, only eight will be identical. By nature's design, a fellow will produce a couple hundred million per ejaculation. A female will produce only several hundred viable eggs (nature design) and, at the very best, of these candidates only four will ever be identical. (She tosses out the other half, as she does not have the cellular resources to create the rest of the cellular 'machinery' needed for a full eight viable eggs that make for fully functional cell to operate when joined with the male's sperm/DNA contribution).

In any event, I have my answer here. Autosomal DNA testing can likely indeed identify a cousin, as the more matches there are the more likely this relationship as the result. However, it cannot identify with any degree of certainty whether or not the cousin lay within your parental or maternal lines. Crossover that occurs countless time between matched XX pairs before a cell results in a gamete prevent such a determination from happening. It is up to the researcher to figure this out (and hope that whatever he/she is proverbially making the decision from traits that are not commonly shared from both parental lines). Shared traits are common within groups sharing the same ethnicity - why they have similar.

Re: Ancestry DNA Question

Posted: 12 Oct 2013 10:12PM GMT
Classification: Query
Lee, mitotic recombination does occur, but it's "rare and abnormal."

http://sekelsky.bio.unc.edu/Research/Mitotic_rec.html

Thus the pieces are larger than you seem to think. Perhaps it would help to look at some real-life examples of how segments are shared between cousins. K&D and K&J are first cousins once removed, and K&L are second cousins once removed. You can see how the amount of DNA has decreased in the more distant relationships. As more generations pass, the amount decreases, but the size of any remaining segments can be long enough to recognize. This is because of the low probability of a recombination event occurring in the middle of a segment.

It's true you can't identify whether a cousin is on the maternal or paternal side with just a single comparison. But people build up connections by testing multiple cousins, some on the maternal side and some on the paternal side.

http://blog.23andme.com/23andme-and-you/23andme-how-to/track...
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