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Chromosome Pairs?

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  • KAM
    replied
    Regarding showing pairs of chromosomes

    Hi,
    Showing pairs of chromosomes on the browser in FT-DNA would be just like at 23nME. It is a good reminder that when you are seeing matches that you have TWO sources for the segment (maternal / paternal) and you can't just assume it is one or the other.

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  • 192971
    replied
    Originally posted by Frederator View Post
    Although FTDNA COULD have decided to display the two copies of each chromosome separately, they didn't.
    If they would show the two chromosomes of each numbered chromosome pair in Chromosome Browser, it would be misguiding, because they really can not differentiate between the two chromosomes. Showing a matching segment to first of the pair would not mean anything else than showing it on the second of the pair.

    ...but hey! FTDNA could show pictures of pairs of chromosomes in CB, but the coloured matching segment bars not on either of the chromosome picture pairs, but between them. Current way is more space efficient, though.

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  • John McCoy
    replied
    The methodology does not result in a single continuous sequence that defines an entire (haploid) chromosome. Rather, the raw data consists of a catalogue of SNP's, and the matching algorithm detects "runs" of varying lengths, which, if long enough, are almost certainly from the same homolog. If you happen to get some good matches, it is possible to infer the sequences of significant chromosome sections. If you don't have good matches, there is no way to know which SNP's came from which parent, or which homolog they reside on. A very peculiar situation, but that's where it stands today.

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  • Frederator
    replied
    I think there is a better answer.

    Although FTDNA COULD have decided to display the two copies of each chromosome separately, they didn't. I think that's because the computer programming algorithim needed to identify matches would be bulkier and less efficient in terms of time and power usage if they did.

    What FTDNA CAN'T DO is identify which matches are paternal or maternal to a user. In fact, each physical copy is probably a mish-mash of paternal AND paternal along different regions. That you have to do for yourself, preferably through phasing, if possible.


    Originally posted by John McCoy View Post
    The current technology cannot distinguish the two copies of each chromosome. The Family Finder test is based on detecting specific but very small DNA sequences, regardless of what they happen to be attached to or how they are arranged. In effect, the result is a catalogue of your SNP's, not a continuous sequence of each chromosome.

    If you happen to be lucky enough to have autosomal DNA results from a set of known relatives on each side of the family, you may be able to infer which SNP's come from which side of the family, and then use that information to deduce relationships of some of your other matches. I have not been so lucky.

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  • John McCoy
    replied
    The current technology cannot distinguish the two copies of each chromosome. The Family Finder test is based on detecting specific but very small DNA sequences, regardless of what they happen to be attached to or how they are arranged. In effect, the result is a catalogue of your SNP's, not a continuous sequence of each chromosome.

    If you happen to be lucky enough to have autosomal DNA results from a set of known relatives on each side of the family, you may be able to infer which SNP's come from which side of the family, and then use that information to deduce relationships of some of your other matches. I have not been so lucky.

    Leave a comment:


  • fmoakes
    replied
    Originally posted by Frederator View Post
    Good catch. I didn't notice that until I ran into the anamolous case of matching A and B on a segment but A not matching B. Confusing!

    I think they did this to save computational power for the matching algorithim, but that's just a guess. Bloody nuisance, though.
    Google Autosomal DNA Phasing for a better understanding.

    Leave a comment:


  • Frederator
    replied
    Good catch. I didn't notice that until I ran into the anamolous case of matching A and B on a segment but A not matching B. Confusing!

    I think they did this to save computational power for the matching algorithim, but that's just a guess. Bloody nuisance, though.

    Leave a comment:


  • ronglong
    started a topic Chromosome Pairs?

    Chromosome Pairs?

    Our cells have 23 pairs of chromosomes but the chromosome browser shows single chromosomes. Disregarding the X and Y, why don't we see two chromosomes #1 - 22? Is the one shown a combination? I hate to appear so ignorant but would someone please clear this up for me.
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