May 07 2008
Whose Y to Use? Paternal Ancestry for Ladies
One 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.
2 Responses to “Whose Y to Use? Paternal Ancestry for Ladies”
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I’m just learning about 23andme, so excuse my uneducated questions, but here I go. I have very few male relatives left. I still have my dad and there is also one of his first cousins (his mom’s brother’s son). They are both in their 90s. What can I learn from either of their DNA? Is it only about their fathers? Since the cousin is on my grandmother’s side, can I then learn about her side of the family? So in order to learn about both paternal and maternal lines on my dad’s side of the family, I’d have to get both their DNA?
Whose DNA would tell me about my mom’s side of the family?
You can actually learn a lot about your own ancestry by looking at the DNA of your dad, his cousin and yourself. Let’s start with you. Your mitochondrial DNA will tell you about your all-female ancestry, i.e., your mother’s mother’s mother’s mother, and so on back a few thousand years (exactly how far back depends on what that ancestry is). Your dad’s Y chromosome will tell you the same thing about his (and thus your) all-male ancestry. And your dad’s mitochondrial DNA will tell you about his mother’s all-female line.
So to sum up, having your dad’s DNA and your own will give you some information about where three of your grandparents’ ancestors came from: both your paternal grandparents and your maternal grandmother.
Your father’s cousin is a bit more complicated. Basically, his Y chromosome will give you a little more another data point about your paternal grandmother’s ancestry. That’s because, even though your great-grandfather’s (your father’s mother’s father) Y chromosome didn’t get passed down to your grandmother, it did get passed to her brother, and then to his son (your dad’s cousin).
I find it really helps to draw a family tree when you think about these things!