Twins & Multiples

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Do Twins Have the Same Blood Type?

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We’ve all seen identical twins who are so similar it’s almost impossible to tell them apart.

But just how identical are identical twins? Do they share any other similarities beyond just looking alike? Do twins have the same blood type? What actually causes this to happen?

Why are some twins identical and some twins not?

First, it’s important to understand what causes some types of twin to be identical and others to not. That’s because there are two main types of twins. Identical and fraternal.

Fraternal twins are caused when two eggs are released, and they’re both fertilised by sperm, and both develop into separate embryos.

Because fraternal twins come from two different eggs and two different sperm, they’re going to have different chromosomes and different genetics, so they’re non-identical.

This isn’t to say that they aren’t going to have things in common, because after all, so do normal brothers and sisters.

Identical twins, on the other hand, come from one egg and sperm, which splits early on in the pregnancy into two embryos, which then go on to form your twins.

Because they come from the same egg and sperm, identical twins start their lives with identical chromosomal and genetic patterning, so the building blocks that make them up will be exactly the same.

However, our DNA changes over time, especially in the womb, where our cells are splitting up hundreds and thousands of times, to go from that initial fertilised egg to an entire person, and because identical twins split incredibly early on, somewhere around the first couple of weeks.

twin baby clothes

There’s a lot of potential for changes to happen in their DNA.

This is why identical twins are never exactly the same, and why in some cases you can get really weird occurrences, like identical twins with different colored eyes or hair.

But there’s some things that identical twins pretty much always share, and some that they don’t. Here’s a list of things that you might not have thought about when it comes to identical twins, and what it means for them.

Do identical twins have the same blood type?

The short answer. Yes. Blood type is entirely determined by DNA, so identical twins pretty much always have the same blood type. But because of the small changes in DNA that can happen in the womb, it’s entirely possible for twins to have different blood types from each other.

Do identical twins have the same retinal scan?

No. The pattern of blood vessels in your retina is partially genetically determined, but is also incredibly complicated and unique to each person, because of the web of capillaries that make up the patterns on your retina.

It’s actually possible for your retina to change over time, but it’s incredibly unlikely and only ever happens because of diseases or damage, so a retinal scan is the most reliable way of telling two identical twins apart!

Can identical twins have the same fingerprints?

This one’s a weird one. The answer is actually yes and no.

Early on, whilst they’re still in the womb, identical twins actually do have identical fingerprints. But this doesn’t last long.

As babies move around in the womb and touch the walls of the amniotic sac, it affects their fingertips, and this is where fingerprints are finalized.

Because of this, because your twins are unlikely to share an amniotic sac, and even if they do they’re going to be touching different parts of it, they’re going to end up with completely different fingerprints.

Do identical twins have the same genetics?

It’s a common trope in crime stories. The identical twins who commit crimes and use the fact that they’re twins and have the same genetics to give themselves an unshakeable alibi and get away with it!

But new research shows that all of this may be a lie. Even though we’ve thought for years that identical twins have identical genetic structure, they might actually have different enough genetics that it’s possible to always tell who is who.

It’s not just the changes that happen in the womb, like we said earlier, either. New research suggests that the DNA you’re born with is not the DNA you die with.

Genetic variations occur throughout our entire lives, whenever DNA breaks after exposure to ionizing radiation and carcinogens. This could even be the reason why identical twins start off being so similar and slowly end up looking different over time.

So now you know. If you ever meet a pair of identical twins and you need a foolproof way to tell them apart, grab your retinal scanner or a fingerprint kit!

How do you tell your twins apart? Is there anything odd that they share, that you really wouldn’t have expected before you had twins? Or maybe your twins are different in a really strange way.

Either way, share it all with us. We love hearing about twin stories, and everything we learn about twins is something else we can share with all of you, our lovely readers!

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