Is Marrying Your Cousin Actually Dangerous?

what did Queen Victoria Charles Darwin and Albert Einstein have in common they all married their first cousins you 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 and 1850 the average married couple was fourth cousins so they had the same great-great-great grandparents genetically speaking that means they shared 0.2% of their DNA not much when you compare it to third second 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 mates 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 one 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 four to seven percent for the general population it's three to four percent 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 [Music]

Channel: Insider Science

Views: 3,617,126

Keywords: Business Insider, Science Insider, Birth defects, Genetics, Evolution, Marriage, Relationships, Cousins, Family tree, DNA, Marrying cousins, Kissing cousins, Genetic disease

Id: sZQs02wRac0

Length: 3min 46sec (226 seconds)

Published: Sun Jul 29 2018