ABOCan you find your blood type in your 23andMe raw data? Mostly, yes
A form asks for your blood type and you guess. Your 23andMe reports never mentioned it, so you assume the test did not look. It did, sort of. The two spots in your DNA that decide the letters are inside the raw data file you can download from your account. With a text editor and the search box, you can read them yourself in two minutes.
How blood type works, in one paragraph
Your red blood cells are covered in tiny sugar tags. One gene, ABO, builds the tool that attaches them. The A version attaches one kind of sugar, the B version a slightly different one, and the O version is a broken copy that attaches nothing. You carry two copies of the gene, one from each parent. Two A copies, or an A and an O, make you type A. B works the same way. One A and one B make AB. Two O copies make O.
In 1990 a team in Seattle found what breaks the O copy: a single missing letter in the gene. Everything after that gap is garbled, and the tool never gets built. That missing letter is what you are about to look for.
Find it in your file
Two searches, one table
In your 23andMe account open Settings, scroll to 23andMe Data, and request the download. It arrives as a zip; unzip it. Our download guide has screenshots.
Notepad on Windows, TextEdit on a Mac. Not Excel, which mangles the columns. Press Ctrl+F (Cmd+F on a Mac).
The letters at the end of that line are DD, DI or II. D stands for deletion, the broken O copy. I stands for insertion, a working A or B copy.
This line reads GG, GT or TT. Each T marks a B copy; each G marks an A copy, or an O, which this marker cannot see.
| rs8176719 | rs8176746 | Your blood type |
|---|---|---|
| DD | anything | O |
| DI | GG | A |
| DI | GT | B |
| II | GG | A |
| II | GT | AB |
| II | TT | B |
If either line ends in two dashes, the chip did not get a reading there, and this trick has no answer for you.
Why "mostly"
Three honest caveats.
Some O copies are not broken in the usual way. A small minority of people carry an O copy without the missing letter. The file would show II or DI for them and the table would say A when the real answer is O. For most people of most backgrounds the table is right, but it is a chip reading, not a blood test.
Chips sometimes misread gaps. A missing letter is harder for a DNA chip to call than a swapped one. A rare misread flips the answer.
A has subtypes. The table does not tell A1 from A2, and it says nothing about the dozens of other blood group systems a transfusion lab checks.
Why the plus or minus is missing
Rh negative usually means the whole RHD gene is absent. That was shown in 1991: most Rh negative people simply do not have the gene. A DNA chip reads single letters at fixed addresses. It can notice a swapped letter or a one-letter gap, but it cannot notice that an entire gene is not there. So no 23andMe-style file tells you plus or minus, and 23andMe is right not to guess.
If you need your blood type for real, a lab needs a drop of blood and ten minutes. Donating blood gets you the answer for free.
Other companies' files differ. MyHeritage files leave out the O marker, so the method does not work there. If your file has both markers, whichever test it came from, it works the same way.
Blood type was the easy part
Two markers for one party trick. The same file holds about 600,000 of them, and a few hundred say something useful about you: how fast your liver clears caffeine, whether milk still agrees with you, which kind of muscle fiber you lean on, whether your body clock runs early or late, how strongly stress lands. Looking those up one by one takes weeks. Reading them all takes about a minute.
Sources
- Yamamoto F, Clausen H, White T, Marken J, Hakomori S. Molecular genetic basis of the histo-blood group ABO system. Nature, 1990. PubMed 2333095
- Colin Y, Chérif-Zahar B, Le Van Kim C, et al. Genetic basis of the RhD-positive and RhD-negative blood group polymorphism as determined by Southern analysis. Blood, 1991. PubMed 1824267
- American Red Cross. Blood types and how common each one is in the US. redcrossblood.org
