Visual phasing is a technique developed by Kathy Johnston and Randy Whited which allows to assign DNA segments of three full siblings to all of their four grandparents by comparing their crossing-over positions on a specific chromosome. (It’s even possible to reconstruct nearly complete DNA profiles of your ancestors using this technique, if you have the possibility to work with five, six or more siblings.)


  • autosomal DNA raw data files of the three full siblings (or more) uploaded to GEDmatch
  • multiple 2nd or 3rd cousins on several ancestral lines available for comparison
  • Steven Fox’s automated Excel spreadsheet (available for download at the Visual Phasing working group on Facebook)
  • advanced understanding of genetic genealogy
  • analytical skills and patience

However, you can also work with two siblings and other close relatives, but it’s a lot more complicated (see examples below). And you can also work with half siblings, but you will only be able to assign DNA segments to two grandparents.


My mother’s and her siblings’ chromosome 1

My mother’s and her siblings’ chromosome 1 using Steven Fox’s excel spreadsheet

Please keep in mind that your Visual phasing results may be incorrect due to hidden recombinations. Such situations occur when two close crossovers of two siblings look like a single crossover for the third, or when very close crossovers “cancel” each other out entirely. In this case, their presence would only be suggested by additional siblings or other matches, because they won’t be visible in the GEDmatch One-to-one comparison images at all.

Here are two examples:

My father’s and his siblings’ x-chromosomes

Hidden recombinations on my mother’s and her siblings’ chromosome 21

LINKS TO MORE CASE STUDIES: – a five part series on Visual Phasing by Blaine Bettinger

Chromosome mapping with siblings – part 1 by Ann Raymont

Chromosome mapping with siblings – part 2 by Ann Raymont

YouTube video by Lars Martin

The Use of Crossover Lines Among Siblings to Determine Segment Matches with Grandparents— Visual Phasing

Double Visual Phasing by Joel Hartley

Not everybody has three siblings to work with. Visual Phasing with two siblings is a lot more difficult, but not impossible, as the following examples show:

Down the DNA Rabbit Hole – Visual Phasing with Two Siblings by Deborah Sweeney

Visual Phasing with Two Siblings and a Niece/Nephew by Leanne Cooper


  1. In your article describing the use of Visual Phasing Spreadsheet V2.3, in Section 2.5 Extending segments, you said the following: “It looks like I’m stuck…..” You extended a color combination of a Red and two yellow segments … by changing one of the codes. My question: are you able to also apply that concept to any other areas where that same combination occurs on the same Chromosome?

    Or, can this be done only once on a partular chromosome?

    Can this technique be used on other color code combinations?

    I enjoyed studying your article. Thank you.

    Ted Richardson

    1. Hi Ted,

      I appreciate your feedback, thank you. No, you can make that arbitrary decision of changing the codes only once on the same chromosome. After that the relationship between the codes on this chromosome will be set. However, if the same situation occurs on a different chromosome you can apply this technique again (because every chromosome needs to be visually phased separately).

      1. Thank you, Eleonora.

        To further my understanding, does this arbitrary decision only apply to Red-Yellow-Yellow color combinations… as was the case in your example?

        Thank you, again.

        1. I’m not sure whether I understand what you mean correctly. The arbitrary decision is independent of a certain color code combination. It’s basically one additional step you can make after you have mapped a chromosome as far as you could using logic.

  2. Hello Eleonora,
    Do you have, or know where to get, a list of the starting and ending positions for the 23 chromosomes?

    There must be a scientific answer to this question, but I can not find it.

    I am nearing completion of an almost-automatic 3-sibling Visual Phasing spreadsheet.

    Thank you,

    Ted Richardson

  3. Hello Eleonora,

    I think that I am ready to beta test my program … Auto Visual Phasing – 3 Sibling Version. I would like for you to try it out, if you are interested. To help you decide, I can first send you a User Guide.

    Thank you,

    Ted Richardson

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