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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

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