Eli5 How come getting blood from someone else doesn’t change your genetics?

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If you’re at the hospital and you get pumped full of blood, how come it doesn’t change your genetics? Is blood unrelated to that sort of thing and I’m just stupid?

In: Biology
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Blood carries your genes, but doesn’t make them. Or in other words, when blood is created it has the genes of whoever produced it, but as it travels around your body it doesn’t change anything because that’s simply not what blood does.

There’s no DNA in red blood cells, platelets, or plasma. Only white blood cells have DNA. Regardless, blood cells don’t reproduce on their own. new blood cells are made in the bone marrow. If you get a whole blood transplant, you’ll have white blood cells from the donor for about about 2-3 weeks and then they die and get replaced by your own new white blood cells made in your bone marrow.

The only way you could wind up permanently changed DNA in your white blood cells is if you get a bone marrow transplant. In that case, the donor bone marrow will continue to make white blood cells using the donor’s DNA.

It’s also important to understand that cells can’t change the DNA of other cells. If you get a bone marrow transplant, only the white blood cells made in your bone marrow will have different DNA. They don’t change your genome in any other part of your body. Same for an organ transplant. Getting a donor organ means only that organ has the donor’s DNA. The rest of you is still you.

New blood cells are made in your bone marrow. When you receive a blood transfusion, those blood cells will never split or reproduce — they’re going to live for a while (about 120 days), happily transporting oxygen for you, and then they’re going to die. Your kidneys will filter the dead cells out of your bloodstream, and you’ll pee them out.

Long story made very short: We get our blood from our DNA. We do not get DNA from our blood.

Not sure if that’s long enough for ELI5, but it’s about as simple as it can be put.

My wife had a blood transfusion at birth, so when her Mother was asked if she had blood relatives she said two instead of three and didn’t include my wife!

There are three reasons why donated blood doesn’t change your results on a DNA test for your genetics or have long-term impact on your genetics:

* Donations are primarily made up of red blood cells, and **red bloods cells do not contain DNA**. So even though *some* cells have the donor’s DNA, *most* do not and it is hard to detect
* All blood cells are eventually replaced. This takes 90-120 days for red blood cells (including the time the cell existed before the blood was given to you). White blood cells have a much larger range of lifespan (20 days to several years depending on the type
* When blood cells are replaced, they are simply broken down and new ones are made by other parts of **your** body so the last of the donor’s DNA will be gone within a few months

Finally, even though those blood cells have the DNA of the donor, they don’t interact with your other cells or existing DNA to change it in any way.

However, **bone barrow transplant** (see [https://medicalxpress.com/news/2018-01-bone-marrow-transplant-dna.html](https://medicalxpress.com/news/2018-01-bone-marrow-transplant-dna.html)) has a more permanent effect on the DNA in your body, since bone marrow makes white blood cells which contain DNA. This is a pretty permanent change.

Bone marrow transplants can affect a DNA test since that bone marrow will indefinitely produce blood with the donor’s DNA, but will not interact with your *existing* DNA. There have been cases where the donor DNA is found in unexpected places (like hair, see ), but the majority of your body still has your DNA, and the two sets of DNA don’t interact.

It has not been found to impact, for example, the sperm or eggs used in reproduction, so kids wouldn’t have have the donor’s DNA mixed up in them

For the same reason that getting a bacterial infection doesn’t change your genetics. Those cells you get aren’t part of your body, they’re just swimming around in it. Humans aren’t just one organism, we’re colonies of trillions of organisms. Some of those organisms, the human cells, are directly related to one-another like a big family. Other organisms, like bacteria in the small intestine, are friends we’ve picked up that help us digest food and fight off mean bacteria, but that aren’t related to us and aren’t passed down to our kids. Yet other organisms, like malaria parasites, are things that live inside us but that we’d rather didn’t do that.

We take foreign DNA inside us all the time, and very little of it modifies our own DNA. The only ones that do are some kinds of viruses, and they only do it to the cells they encounter, so only a small portion of the body is modified by those viruses. On average, your DNA remains unchanged.

It’s not stupid at all. After all, you’re taking a piece of someone else and putting it into you. As others have said, there’s no DNA in red blood cells, so there’s no chance of that at all in this case.

But, your question gets deeper – can ANY kind of transplant/transfusion change your genetics? And this answer is no*.

*That is, it won’t change your overall genetics, because every cell in your body has your blueprint, and those won’t change if another part of you is replaced. But if you had a lung transplant? The genes of your lungs WOULD be different than the genes elsewhere in your body! Same for your kidneys, heart, and other organ transplants. If you get Carol’s lungs, then they’ll live and reproduce lung tissue and every new cell that’s made to replace old and damaged lung cells will have Carol’s genes in them.

In fact, this is a big deal in transplant medicine. Some people can’t donate organs because of it, and if there’s a risk for certain genetic diseases they’re tested for and screened out in order to minimize risk to the person getting the transplant. Crazy, huh?