DNA Testing - Y DNA

[Redroger]

....There is one person with whom I match 33/37 markers, but FTDNA say since we are different haplotypes we cannot be related. My response is that as there are only around 550 carriers of the surname (under 300 male), surely the different haplotype is an error in their test. ....

That sounds very odd to me

I won't say odd, if the surname had been Smith etc. I wouldn't even have thought of querying it, but with a fairly rare surname I do really wonder.

[Tricia_2]

Good luck sorting it out

[Redroger]

Problem is they want money to do a retest, which they MIGHT refund if they are wrong!!

[Tricia_2]

Genealogy can be a very expensive hobby ~ especially when genetic research is involved.

[Guy Etchells]

Dna cannot prove a person is a father of a child but can disprove the possiblity a person is the father od a specific child.

One has as much chance tracking males carrying the same surname or even males in the surrounding area as using DNA to prove a lineage.

It can be a useful tool to disprove a lineage.
Cheers
Guy

[Tricia_2]

Hi Guy

Thanks for responding.

Are you saying that, even if two men have identical DNA, they may not be related??

Or are you saying that you cannot tell, exactly, what the relationship is?

[Nick29]

The only people that can have identical DNA sequences are identical twins, and even that is quite rare, because of genetic mutations that can occur with time.  So, the father of a child will not have identical DNA to the child, but he should carry many significant identical DNA sequences as the child. The full human DNA sequence is 3 billion base pairs, and to test for matches in the complete sequence would be logistically impossible.  So DNA tests only look at specific areas of the DNA sequence, and the numbers of matches in those selected gene pairs.  As the number of matches increases, then the probability of an ancestral match increases, but (as Guy said) it is impossible to prove 100% that one person is related to another, but quite often it's very easy to prove that people are not related due to lack of matches.

[Tricia_2]

Hello Nick and Guy

Thanks for your comments!

Ok, now I'm really confused. 

Based on my (rather ancient now) school genetics classes, and on info gleaned from various books, documentaries and DNA testing sites, I was under the impression that Y-DNA, as passed from father to son, to grandson, etc, etc, was identical, apart from the odd mutations that occur, from time to time, along the way.

Also that Mitochondrial DNA, passed down the female line, would be either identical, at each generation, or slightly altered, also as a result of mutations.

I know that I am becoming confused, but are you saying that I have been misled? 

Thanks!
I think that I need to know what  can discover from DNA testing

[Craclyn]

You are correct in your understanding of Y-DNA and mtDNA. Nick's comment seems to relate more to autosomal DNA which is a combination from the parents. Siblings will inherit different segments unless they are fraternal twins. The 4th type which has yet another set of combinations is the X-chromosome. Useful in determining which ancestral lines you share with someone as it cannot be passed through 2 males in the line.

If you just focus on Y-DNA and mtDNA then you can only follow two lines (paternal and maternal). To find matches with all your other ancestral lines then you also need to look at autosomal DNA.