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  • What did Queen Victoria, Charles Darwin and Albert Einstein have in common?

  • They all married their first cousins.

  • You'd think Darwin of all people would know better.

  • After all, mating with a close relative passes on bad genes that leads to deadly genetic mutations.

  • Right?

  • Today, marrying your first cousin is illegal in 24 US states.

  • But for most of Western history, people had to marry whoever lived nearby, which oftentimes meant marrying within the extended family.

  • In fact, between 1650 -1850, the average married couple was fourth cousins.

  • So they had the same great, great, great, great grandparents.

  • Genetically speaking, that means they shared 0.2% of their DNA.

  • Not much when you compare it to 3rd, 2nd and especially first cousins.

  • And the more DNA you share, the greater chance your offspring will have a genetic disease like cystic fibrosis or sickle-cell anemia.

  • But here's the thing, you don't have to be sick in order to give your child a genetic disease.

  • Take cystic fibrosis. It's caused by a defect in the CFTR gene, but you need two copies of the defective gene to actually get the disease.

  • So if you only have one defective copy, you are unaffected. Instead, you are what's called a carrier.

  • Now, if one carrier meets with a non-carrier, there's no risk of the kids getting sick.

  • But when both parents carry a defective copy of CFTR, then the kids have a 25% chance of inheriting two copies of the gene and having the disease.

  • So to see how dangerous it is to marry your first cousin, we need to calculate the chances that two first cousins both carry a copy of the same genetic disease.

  • Since they share a set of grandparents, we'll start there.

  • Now, it becomes a game of what ifs: what if both grandparents are carriers versus just one?

  • What if one of their Children is a carrier versus none at all?

  • And what if those Children marry other carriers or not?

  • It can get very complicated very quickly.

  • But scientists have crunched the numbers and it turns out the risk that the cousins have a kid who inherits a genetic disease is 4 to 7%.

  • For the general population, it's 3% to 4%.

  • So, not a big deal. Right?

  • Here's the catch, that's the odds for one genetic disease.

  • But there are thousands that could be hiding in your family tree.

  • Plus, if your kids also marry their first cousins and their kids marry their first cousins, it's a recipe for disaster,

  • because instead of introducing new, potentially helpful genes into the family gene pool, you're recycling the old and possibly dangerous ones.

  • Take Emperor Ferdinand the first of Austria, his parents were first cousins twice over.

  • And when he was born, he wasn't especially healthy.

  • So as far as marrying your cousin is concerned, you shouldn't make it a family tradition.

  • What interesting things have you found out in your family tree?

  • Let us know in the comments.

What did Queen Victoria, Charles Darwin and Albert Einstein have in common?

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