Whose Y to Use? Paternal Ancestry for Ladies

gus.jpgOne of the most exciting parts of 23andMe’s Personal Genome Service™ is discovering your genetic ancestry. Suddenly your family tree has branches that reach back thousands of years into the prehistoric past.

At present, 23andMe customers can trace two branches of their genetic family tree – one that follows the all-female line on the maternal side (through mitochondrial DNA) and another the all-male line on the paternal side (through the Y chromosome).

Not all DNA is created equal, however: males have both mitochondrial DNA AND a Y chromosome, so they can trace both their maternal and paternal ancestry. Females, who have mitochondrial DNA but no Y chromosome, can trace only their maternal ancestry.

So how can females discover their paternal history? One solution is to ‘borrow’ the Y chromosome of her most immediate paternal ancestor – her father. A female can have her father send his own DNA sample to 23andMe, then examine his Y chromosome as a way of understanding his paternal ancestry and her own.

But what if a woman’s father can’t or won’t share his DNA? By sharing 23andMe accounts with the right male relative, a woman can still discover both her maternal and paternal ancestry.

So whose DNA can a female customer use, besides her father’s? It could be anyone who shares his Y chromosome – her brother, paternal uncle (father’s brother), or even paternal grandfather (father’s father). The chart below illustrates some of the possibilities in one woman’s family tree; male relatives who share her father’s Y chromosome are depicted in blue.

You may look at the chart and ask: Why not her son’s Y? After all, he’s a male relative, too. But even though a mother shares 50% of her genes with each of her children, only fathers pass Y chromosomes to their sons. So any examination of her son’s Y chromosome would yield not her father’s paternal history, but her husband’s.

The woman whose family tree is shown here (“Me”) could determine her paternal ancestry using the Y chromosomes of males who are colored blue.

  • Scott23H

    Her ancestry is a mix of both her father and her mother. Although we cannot easily identify what came from her father, there are ways to do that. If her mother were to test for instance she could then look at split view in the ancestry composition tool and see what ancestry came from her mother and what came from her father. The reason testing her son wouldn’t help is that the Y chromosome is passed on from father to son. That traces the paternal line. So her son didn’t get his Y from her father but from his father and his father’s father.

    • kitty

      Ok, but then what if the woman who has the father who was adopted but died also has no sisters and her mother is dead also ? Then she has only herself to take the test to find out what her father’s ancestry was, wouldn’t there still be a way since she would have half of what he was in her genetic pattern ?

      • Scott23H

        Hi Kitty,
        That will be much more difficult. It will take using other information she may have about either her mother or father. It may be that she can look at her DNA Relative matches. Some of those will be from her father’s side. Looking at how those matches cluster and the ancestry of those individuals may help. Again it will take some triangulating of information.

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