how to determine lineage

[annalubov]

How to figure out this problem: mother/daughter tested, both have of course X chromosome (haplo is D4). On Gedmatch largest X match was of different haplo T1. Having X matches but have completely different haplgroup? Can someone help me to understand it ?

[msmarjoribanks]

Significant X match for a woman need not have the same haplo, because X match and mtDNA are different.

For example, mother and daughter share mtDNA AND are an X match.

Daughter and father do not share mtDNA but are an X match (daughter gets X from both parents).

Here, the daughter and mother both match another person, but the other person need have gotten his or her matching X segment from someone sharing a matrilineal line with them. For example, the mother and daughter have a matching X segment from the mother's father, someone with whom they would not have an mtDNA match. If the other person matched is a woman, that person's matching X segment could be from her father, so again would not go with matching mtDNA.

You can simply rule out that this person is a matrilineal match.

Hope that makes sense.

[geebee]

The same thing is true for males. Although my eldest brother inherited both his mtDNA haplogroup and his single X chromosome from our mother, she didn't get both from the same source.

Like everyone else, of course, she inherited her mtDNA haplogroup from her mother. But the X chromosome she passed on to my brother contained DNA only from her father. In other words, she passed on an unrecombined copy of the same X chromosome she inherited from her father -- which he, in turn, inherited from his mother.

This is not the only time she passed on an unrecombined X, either. One of my sisters also inherited a maternal X chromosome with no contribution from our grandmother. As a result, her X chromosome has half identical matching with our brother across the entire chromosome.

My own X does contain some DNA from our grandmother, though not much: only about 20 cM surrounding the centromere. The rest is from my maternal grandfather.

One way the X chromosome can be very useful in genealogy is that it has vastly fewer possible contributors as compared with other chromosomes. It can be helpful to fill out a chart like the one found here. Just remember, not everyone who is a potential contributor to the X chromosome will necessarily be an actual contributor.