Transcript generated automatically by AI and may contain errors.
Chapter 1: What is the main topic discussed in this episode?
Welcome to the Rest of Science. I'm Hannah Fry. And I'm Michael Stevens. Today, I want to tell you about something I've discovered.
Chapter 2: What new method for creating twins does Michael discover?
Go on. A new way to make twins. Is it ethical? Oh, it's ethical. It's not easy. Okay. There's two ways to make twins.
Chapter 3: What are the ethical implications of this new method?
Yeah. And the first way is the normal way. You and your partner just really hope that that zygote splits into two babies. Genetically identical. Genetically identical individuals. The second way is for you and your partner to have about 70 trillion children. Okay. That sounds like quite a lot of work. It's not that bad. All it requires is birthing 70,000 children a second.
What, for your entire fertile life? Well, I mean, for your entire fertile life. Not mine, my partner's, luckily. You're not going to get much else done. No, no, but wouldn't it be cool? I'll talk about how this works in a moment.
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That, I mean, I think for all of us went in a different direction than we were expecting. Well, there's two kinds of twins. There's the fraternal twin, which is also called the dizygotic twin. And what happens there is that two zygotes form. What's a zygote? When the sperm and the egg mix, they make a zygote. That's the very first stage.
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Chapter 4: What role does the dark genome play in our biology?
But we can also grab on to the birthday problem. You don't actually need to have 70 trillion kids in order to get a specific possible kid. You'll have to try like 70 trillion times. But to get kids such that you can find a pair that match, you only need to have about 10 million kids. Oh, hang on. Suddenly this sounds achievable. Suddenly it's looking like it's going to happen.
10 million children. The chance that there will be a pair that have the same genome is about 50%. So it's like a coin flip.
Now, OK, you can't compare that 10 million number to 110 billion, right? No, because this is 10 million children from the same parents. But even so, actually, suddenly the chances of two siblings being essentially very, at least very, very, very close, if not completely identical, despite not having come from a single zygote, I mean, starting to look quite likely.
But here's the thing that makes it even more complicated. I'm talking about people sharing their genome. But really, when it comes to looking at them, it's the phenotype that makes them unique. It's the expression, the behavior, the things that we can observe. And someone can have a very different genome than someone else.
And yet their nose, their eyes, their hair, all that stuff can be really similar. And that's why siblings so often look alike, even though we can genetically tell them apart.
I can open my sister's face ID on her phone. Are you serious? She finds it extremely annoying, by the way. Not that I'm opening her phone all the time, just that she shares my face. I would not confuse you two though. No, no, you wouldn't confuse us, but in like our mannerisms and on Face ID. Yeah, Face ID. Because Face ID is, a lot of it is about your orbital bone.
Oh, is it?
Yeah. Because it's a structure that doesn't change.
My sister, I don't think she looks anything like me, but I think our mannerisms, like you said, are very similar. My daughter picks that up. She only wants me or my sister to read her bedtime stories because she says that we deliver them in the same way. Amazing. I guess so. Or is it? Or is it, says my sister and me.
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Chapter 5: How do monozygotic and dizygotic twins differ?
You're getting somewhere between 23% and 27%. The half you get from your mom could be like a little weighted towards her dad and less her mom. For example, your great-grandchildren. will only have between 9% and 14% of what makes you unique. By seven generations, your seven great-great-great-great-grandchild is statistically no more like you are right now than a stranger on the street.
How many generations did you say?
Seven. Really?
By seven. After seven generations, we reach a point where it's possible for your progeny to have absolutely none of your personal genetic variation.
That's so interesting. You know, I've thought this quite a few times actually about ancestors, right? So if you go seven generations back, because I've done some work in the past where I've tried to find their names and try to find out where they're from and all of this kind of thing. Let's think seven generations back. So we're talking about 1700s or so, maybe a little bit earlier.
I guess it'd be like almost 200 plus years ago.
Yeah. Yeah. OK. I don't feel like I have an emotional connection to those people. You know, like I can hear about their story, but I don't feel emotionally connected to their plight in the same way as I do, you know, when I look back to sort of my great grandparents, for instance.
But now what you're saying is, I mean, that's fine because I don't even have a sort of genetic connection to them either.
I mean, you might, but it's going to be small, but it could very potentially be zero. Seven generations is the first distance, the closest distance at which we can expect 0% of the personal genetic variation to have persisted. But if you go back 11 generations... 70% of your ancestors from 11 generations ago are not in you at all.
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Chapter 6: What is the concept of doppelzygotic twins?
And again, twins don't share their DNA exactly. This is like a fun little party thing to bring up if you want to be pedantic because of mutations that happen epigenetically through life. They're not going to be exactly identical. Also, they have different fingerprints. We've talked about this before. Fingerprints are not designed by your DNA. They're not coded by a gene.
They just form randomly in the womb. So you can tell twins apart by their fingerprints. Twins make for a really interesting case because which twin can claim that they own the genome? When would this even come up legally?
Like if one set of a twin was like, hey, I want to sell the personally unique part of my genome for this company to create digital versions or even real flesh and blood versions like clones of me, would the other twin be like, Uh, but I don't want that. And I'm the same in appearance in many ways. People are going to confuse me with all these like clones that you're allowing to have made.
I feel like courts would have a pretty easy time with that one.
What saying no, you're not allowed to.
I think veto power would be given. But what can they do with let's start with just cells. What can they do with my cells? We've already talked about body parts. People can do a lot with my body parts after I'm dead. But what about while I'm alive? They don't take a body part. They just take some cells from me. What could they do with it? What could they do with it? Would they still belong to you?
Would they still belong to me?
Well, the thing you're describing has actually happened, right? In the case of Henrietta Lacks. That's right. Very famous story.
And we'll come to it after the break. Thank you.
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