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General => Ancestral Family Tree DNA Testing => Topic started by: david64 on Friday 10 January 14 20:31 GMT (UK)
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Evening,
I have had two test done at FTDNA (autosomal). I am just looking at the X-DNA, looking for links.
Could someone tell me: Is X-DNA only inherited as show in this chart?
http://www.dnainheritance.kahikatea.net/x_inheritance.html
And will X-DNA be present from each line shown in that chart? Or is it only inherited from some?
In particular, I am interested to know if this could help with a line of inquiry. I am looking for the name of my father's mother's father. My father has taken an autosomal test. The above chart appears to show my father will have inherited X-DNA from him.
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Further, attached are the main X-DNA matches. Does the longest CM here signify anything that could be considered close ?
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Yes that chart sums it up well
A female has two X chromosomes one she inherits from her mother and one she inherits from her father
A male has one X and one Y chromosome. He must inherit the Y from his father and so the X must come from his mother
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Your father got his X chromosome from his mother. And she got one X chromosome from her mother and one from her father. So, your father could have gotten his X from his mother's father. However, keep in mind that chromosomes do not pass from one generation to the next 100% intact because the process of 'crossing over' during meiosis recombines the genes on any pair of chromosomes and so what gets passed on is a mixture of genes on sort of a hybrid chromosome.
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Thanks for your replies.
So does this mean my father could have zero X-DNA from his mother's father?
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Thanks for your replies.
So does this mean my father could have zero X-DNA from his mother's father?
At least hypothetically, yes, if there was no crossing over of the X chromosomes during meiosis and he wound up with the one from his mother's mother.
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http://www.broadinstitute.org/~sfs/nrg_Xchrom.pdf
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Thanks again.
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A 1 Centimorgan is a region where there is a 1% chance of a crossover in one generation. However for X data this can only apply to inheritance from a female since inheritance from a male's X DNA never has crossover (nothing to change to). My guess would be that the autosomal rules for number of generations back estimate should be interpreted as number of inheritances from females in the chain of inheritance from males and females. Note that centimorgans do not tell you how much data you need to feel that a match is real, i.e. if you sample more data will it still look like a match. Number of SNPs is a better guide to confidence that the match itself is real and my experience is that half of the time even real matches need to be trimmed a little. Chromosome 6 matches seem take more data to eliminate false matches probably because it is influenced by selection pressure. My guess would be that there is more similarity in people's X DNA so it probably requires a little more than the 1000 SNP minimum that I use as a rule of thumb on most autosomal DNA. I have tested my 1000 SNP criteria using multiperson matches and it seems to work okay for autosomal DNA not counting chromosome 6.