What's hidden in your chromosomes?

DNA & Genealogy

X-DNA's helpful inheritance patterns

When you test your autosomal DNA, your X-DNA is also examined and included in your raw data &/or match results.  When you match someone on your autosomal DNA and also share segments on the X-chromosome, the unique inheritance pattern of X-chromosomes can help isolate your common ancestor to particular lines of your ancestry.

 

X-Matches in autosomal results

Family Tree DNA's Family Finder test identifies X-Matches with people you already match via your autosomal DNA, and clearly displays them in your match list (as below).

You can also view the X-match detail in the FTDNA chromosome browser, and download all chromosome browser data to Excel or other software or sites for further analysis if desired (eg. GEDmatch).

 

X matches on FTDNA's Family Finder

 

23andMe X-DNA can be viewed in the 23andMe chromosome browser or downloaded, but only for those matches who choose to share genomes with you.  The raw data can be transferred to GEDmatch for comparison with other kits in the GEDmatch database.

AncestryDNA does not provide or show any X-DNA information, so X-chromosome information can only be accessed by transferring a copy of the raw data to FTDNA or GEDmatch for analysis.

 

X-Chromosomes

Your gender is determined by the X and Y sex chromosomes: chromosome pair number 23.

Males inherit a Y chromosome from their fathers and an X chromosome from their mothers.  So all their X-DNA is inherited from their mother.

Females inherit an X chromosome from their fathers, and an X chromosome from their mothers.

 

X Chromosome Inheritance

(Click on image above to open in a new tab, then right-click to save a copy if desired)

 

A mother contributes an X chromosome that is usually a recombined mix of both of her X chromosomes (but not always), and fathers contribute their whole X chromosome intact to their daughters.

 

Because males only inherit an X chromosome from their mothers, if a male has an X-match in his DNA results, the shared ancestor must be on an ancestral line that follows the male X-inheritance pattern, as below (in green):

 

X-chromosome Inheritance Chart - Male

 (Click on chart above to open a higher resolution image in a new tab, then right-click to save a copy if desired)

 

Because females inherit X chromosomes from both parents, if a female has an X-match in her DNA results, the shared ancestor must be on an ancestral line that follows the female X-inheritance pattern, as below (in green):

 

X-chromosome Inheritance Chart - Female

(Click on chart above to open a higher resolution image in a new tab, then right-click to save a copy if desired)

 

X-DNA cannot be passed down through two successive male generations.

 

Because some X chromosomes pass down intact (through males) and skip a generation without recombining, and others are recombined (through females), the average expected percentage of shared X-DNA at each generation varies depending on the branch of the pedigree chart.

 

X-chromosome percentage inheritance chart - Male

(Click on chart above to open a higher resolution image in a new tab, then right-click to save a copy if desired)

 

Compare the percentages across the same generations below.

For example, at the great-great-great-grandparent level, notice how the expected percentage of inherited X-DNA is only 3.1% on the far right direct maternal line, versus 12.5% on the left-most paternal line (and some other lines) at the same generation level.

 

X-chromosome percentage inheritance chart - Female

(Click on chart above to open a higher resolution image in a new tab, then right-click to save a copy if desired) 

 

With no X inherited from some ancestors, varying amounts inherited from others, the randomness of DNA recombination at each generation, and occasional sticky segments passed down intact over several generations, X-DNA can be quite unpredictable and difficult to interpret exactly where it came from.

It is common to share segments of X-DNA with people who share no significant amount of autosomal DNA.

Males generally get far fewer X-matches than females.

X-DNA's best and most practical use is for isolating matches to particular family lines, even though the amount inherited cannot tell you from whom or how far back it came.

Nor can the absence of any X-DNA disprove your relationship (except for immediate family members - see below).

 

Download link for Excel spreadsheet for X inheritance pattern male & female surnamesExcel Surname Template

Click the image to the right to download an Excel spreadsheet surname template to create your own X inheritance pattern pedigree charts - create one for each person that you test (separate sheets for male & female charts).

 

 

 

Practical uses of X-DNA

  • If a male shares X-DNA with a match, then the ancestor in common will be on his mother's ancestral lines, according to the X inheritance patterns in the 'Male' charts above.
  • If siblings have tested their autosomal DNA, and a brother has X-matches in common with his sister(s), then the sisters will know that those particular X-matches must have come from their mother, as their brother could only have inherited them from their mother
  • If brothers share very little X-DNA with each other, one would have inherited most of his X from his mother's father and the other would have inherited most of his X from his mother's mother, or they inherited the exact opposite of a recombined X.
  • If brothers share most of their X-DNA, they would have inherited it either from the same maternal grandparent, or the same or very similar recombined X from both maternal grandparents.
  • If half sisters with the same mother share very little X-DNA with each other, one would have inherited most of her X from her mother's father and the other would have inherited most of her X from her mother's mother, or they each inherited the exact opposite of a recombined X.
  • If half sisters with the same mother share most of their X-DNA, they would have inherited it either from the same maternal grandparent, or the same or very similar recombined X.
  • A daughter will share a whole X chromosome with her father.
  • Full sisters will share a whole X chromosome, from their father.
  • Half sisters will share a whole X chromosome if they have the same father.
  • You can attribute X segments to particular grandparents by comparing your X-DNA with cousins and other close relatives from each side of your family.
  • Don't forget to ask your match to look at the charts above and work out which of their lines you could match them on, to narrow down the possible branches from both sides of the family!

 

BACK TO DNA HOME

 

Useful Links

 

 

Link to Facebook Group - Using DNA for Genealogy - Australia & NZ

Facebook group - DNA for Genealogy UK

 

 

23 Pairs of Chromosomes. 1 Incredible You. Get your DNA story at 23andMe.com.

 

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  • Thank you, Jo - I'm glad it will be helpful to you and your readers :)

  • Pamela Bangs

    Thanks so much for your help
    Pam

  • My Dad has two a female 2nd cousins and one Female 3rd Cousin all who share X DNA with him. All of these cousins are descended through his Great x 2 Grandmother, the other is as well but only through the male line as in her Great Grandfather to Grandfather to Father how is it possible for Her to show a X DNA match with the others. I copied the chromosome browser from FTDNA for one of the 2nd cousins who I knows decent I can confirm and it shows on the X Chromosome all 3 matching at exactly the same point and same length. My Dad is on the X Chromosome too but in two different places and not where the Females are.
    Hoping you can help
    Thanks Trish

  • Hi Trish, Your cousin who is related through her male>male>male ancestors must be related to your father through another ancestor as well, as a male cannot inherit any X-DNA from his father. Their connection on the X chromosome could be from further back than you or she have researched. Even though on the chromosome browser you see each of these cousins overlapping on the same segment, they may not necessarily match each other on the same segment, so that is what you need to check next, from their accounts (if you are the admin) or ask the cousins to check. Or use Gedmatch to compare each against each of the others. :)

  • If I have a 43 cm autosomal match on gedcom, but no match on the x, does that mean that we are not related?

  • Hi Claudia, you should be related - and 43cM is a good autosomal match. The absence of any X-DNA match does not mean you are not related, and cannot rule out relationships. The X-chromosome is just another chromosome that you may match on, but it has its own unique inheritance patterns. So if you do have a good-sized segment of X-DNA (and particularly if you also share some autosomal DNA), it may help you identify which branch of your tree you match on. Good luck :)

  • One of My daughters did not get any X DNA From my mother only from my father"on my side of the genetic tree"
    From her Grandpa my Dad she got A {2040.8 Total cM} {176 largest cM} 1.4 Gen X {196 Total cM} {196 largest cM}
    From her Grandmother My Mother she got {1560.7 Total cM} {largest cM 138.4} 1.6Gen X {0 Total cM} {0 largest cM}
    Me to my dad.. A{3587.1Total cM} {largest cM 281.5} 1Gen X {196 Total cM} {196 largest cM}
    Me to my Mom A{3586.3Total cM} {largest cM 281.5} 1Gen X {196.1 Total cM} {196.1 largest cM}

  • Louise Coakley

    Hi Ann, Yes that happens quite often and is very interesting - thanks for sharing. :)

  • Tonia Bootle

    Hi Louise,
    Thanks for this article, it was so easy to understand. I'm new to this, and recently had my brother tested also through 23andme, as I'm trying to find out who my biological grandfather was. I ran his raw data through GEDMATCH, hoping to identify a few X matches (which would only be mum's side), and when I ran the 'one to many' report, there was only 1 match for his X data - out of 2000 matches! Can this be accurate? I knew this process would be similar to finding a needle in a haystack, but only 1 in 2000? Is there something I'm missing here? Is this another area of his data I should be focusing on or drilling down on through another report or tool? I'm so excited to finally be able to start researching, but also overwhelmed, so any advice you could give me here would be greatly appreciated! :)

    Rated 5 out of 5 stars
  • Hi Tonia, Thank you for your message. Before running the 'One-to-many matches' report on Gedmatch, did you select the ‘X’ version of the report, or the regular ‘Autosomal’ report and search or sort by the ‘X’ column? Males generally get very few X-DNA matches, but the specific X version of the 'One-to-many matches' report usually finds a lot more, even if they share no or very little autosomal DNA, as they are often hidden below the 2000 cutoff of the autosomal report. I hope that helps? Good luck! Louise :)

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