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Introduction to FTDNA X-Chromosome Segment Matching

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  • Tenn4ever
    replied
    Should two full sisters match exactly on the X chromosome?

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  • Kathy Johnston
    replied
    Originally posted by FranM View Post
    What are the implications of a match or lack of match on X? Is this part of autosomal DNA?
    There are 22 pairs of autosomes and a pair of sex chromosomes. The sex chromosomes (X and Y) are not autosomes. A male gets an X from his mother and a Y from his father. A female gets an X from her father and another X from her mother. The autosomes and sex chromosomes are all found in the nucleus of the cell and separate from the mitochondrial DNA.

    The X chromosome pattern of inheritance is similar to autosomal DNA but there can never be two males in a row (father to son) because a male does not give his X to his son. Rather, he gives his Y to his son. So if you want to find a common ancestor who carried the X, you need to map out your pedigree using only the X pattern of inheritance. If you are female, use the female focus chart here to list your ancestors:
    http://debbiewayne.com/search_custom.php

    You will see there are no two males in a row (son to father) going back in time. Entire lineages can be eliminated from the pedigree when trying to find an X ancestor in common.

    A lack of a match on the X does not mean much because some siblings will not match on the X. Full sisters always match each other however because they each match a whole X coming from the father. That is the only time you can rule out a relationship. You can't be full sisters without an entire X match. Females who are half-siblings cannot share a father unless they match a whole X chromosome.

    At FTDNA, the X has been added to the chromosome browser and you don't have to order any special test. Just look at your Family Finder results. Be sure to set the segment size higher than 5 cM (preferably 10 cM). Right now you can't just look at a strong match on the X without also having an autosomal match with the same cousin because there is no chromosome browser here that separates out the X matches from the autosomal matches. You would have to upload raw data to a third party site to look for X matches alone. Some people can match on the X without a significant match on the autosomes. Those people are not on your match list at FTDNA.

    Most X success stories involve lines that have given you both autosomal matches and X matches through some of the same ancestors during recent history. That is simply because you have more DNA in common (and more segments) with a closer cousin. X lineages certainly can be helpful in breaking through brick walls.

    Kathy
    Last edited by Kathy Johnston; 19 January 2014, 11:41 AM.

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  • Kathy Johnston
    replied
    http://www.thegeneticgenealogist.com.../NewChart5.jpg
    gives some probabilities for a male.

    A solid match on the X chromosome allows you to hone in on the lines that are most likely to give you a piece of the X for both you and your matching cousins.

    A match on the mitochondrial DNA can be very distant in the past, often hundreds to even thousands of years.

    The cousin-ship can be difficult to predict even with solid X chromosome matches. If you have many autosomal segments plus a strong X segment match (> 10 cM for example), then there often is an ancestor within a genealogical time frame that appears within the pedigree showing the X inheritance pattern.

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  • FranM
    replied
    Implications of a match on X?

    What are the implications of a match or lack of match on X? Is this part of autosomal DNA?

    Leave a comment:


  • Aroldanf
    replied
    X-chromosome vs. family tree matches

    Basic questions:as a male, genetically speaking, is my relationship with my family tree matches closer than those stablished via x-chromosome matches? Are mtDNA matches genetically closer than x-chromosome matches? As you can read, I'm just trying to make sense out of the raw data. Thank you for your reply!

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  • Rebekah Canada
    replied
    Introduction to FTDNA X-Chromosome Segment Matching

    X-Chromosome Matching at FTDNA (P2 of 2)

    Moving to the Advanced Matching page, X-Chromosome matches have also been integrated.



    X-Match is an option that can be checked alongside other types of testing.



    I will let everyone know when this is pushed live. Enjoy! Please let me know about questions, bugs, or improvement requests!

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  • Rebekah Canada
    started a topic Introduction to FTDNA X-Chromosome Segment Matching

    Introduction to FTDNA X-Chromosome Segment Matching

    X-Chromosome Matching at FTDNA (P1 of 2)

    This week’s big release is X-Chromosome matching. We have fully integrated it into Family Finder matching.

    Here is the menu link to the Family Finder Matches menu.



    On the Family Finder Matches page, there is a filter to show only X-Matches.



    When you use the X-Match filter on a male Family Finder kit, you
    should get only matches from the maternal X-Chromosome.



    Next, like other Family Finder Matches you can expand the advanced bar for a match and click to add the match to the Compare in Chromosome Browser list.



    Matches are added to the Compare in Chromosome Browser list. You could go right to the Chromosome Browser by clicking on the compare arrow at this point.



    Next we can also go right to the Chromosome Browser.



    The Chromosome Browser also lets you filter the match list by X-Matches.



    Here are three immediate relatives. The first two share X-Chromosome DNA. The third (green) one does not.



    When we scroll down to the X at the bottom, we see that X-Matching is displayed for the first two but not the third.



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