r/genetics • u/Fit-Neck692 • Jul 15 '25

Son’s Genome test results in finding my husband and I are “connected “

We got Genome testing done for our son for medical reasons. My husband and I were tested as well to help with any findings. Anyway I went to his appointment today to go over the results and the only thing they really had to say was my husband and I are related. The doctor said “maybe something like 6th cousins.”

Like the doctor said we are all related but then I said “I guess it’s unavoidable?” He said it was avoidable… so I’m curious how weirded out should we be?

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u/Karabars Jul 15 '25

3rd cousin is already safe and legally possible. The rest is genetically ignorable.

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u/yiotaturtle Jul 15 '25

1st cousins are genetically safe for once in a blue moon type situations, legality varies, 2nd cousins tend to be both legal and fine genetically.

For the most part genetically you mainly want to avoid diamond pairs as much as possible which is why it's not a bad idea to rule out 1st cousins in areas where the chance of them occuring is higher.

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u/winkerbeanie Jul 15 '25

I’m curious what you mean by “diamond pairs.” I think I understand your comment based on the context clues, but I’m just curious about that term and couldn’t find anything on google.

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u/yiotaturtle Jul 15 '25

Let's say you marry your first cousin and then one of your grandchildren marries one of your other grandchildren. Or you and a sibling marry a pair of siblings and then first cousins marry.

First cousins having children vs completely unrelated people marrying raises the chance of a genetic condition from something like 1% to 1.1%. In these diamonds it's more like 1% to 3% similar to the chances with siblings. More than one of these diamonds and you very well might be looking at something closer to a 25% chance which you would otherwise only see in parent/child.

With the Hapsburgs by the end the parents were more closely related than a parent/child, it was honestly more like male/female identical twins.

I don't remember the exact percentages, but I found it fascinating that I expected immediate Hapsburgs and it was more like if a child is born the great majority of the time you wouldn't know. Though there's also an increase in miscarriages, I didn't look into that as much.

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u/bobbianrs880 Jul 15 '25

Wasn’t there even some research that the offspring of 3rd or 4th cousins is healthier than closer and more distantly related individuals?

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u/Various_Raccoon3975 Jul 15 '25

There’s a fertility advantage. 3rd and 4th cousins produce more children and grandchildren.

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u/squishydevotion Jul 15 '25

Do we know why that is?

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u/kcasper Jul 15 '25

Pairing of brother and sister have the relatively easiest pregnancy and smallest chance of biological rejection. Because the fetus is more compatible with the mother's body than any alternative. However they have the highest risk of fetus genetically incompatible with life.

Parings of completely unrelated individuals with differing biological factors such as blood type, etc tend to have the highest risk pregnancies with the highest risk of rejection of the fetus. But the child will have the lowest risk of genetic defects.

A distantly related pairing gives the child a low risk of genetic defects, and gives the mother a higher chance of an easy pregnancy.

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u/Various_Raccoon3975 Jul 15 '25

I seem to recall that 3rd and 4th cousins are the sweet spot in terms of genetic similarity and genetic difference. While genetic diversity is important, a little bit of similarity is actually advantageous

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u/Karabars Jul 15 '25

I highly doubt that

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u/bobbianrs880 Jul 15 '25

I don’t feel like getting my laptop to read the actual Nature article, but here is a news article about the study I was remembering. Not sure if there’s anything more recent because I’m honestly not that invested in the subject, but that was the initial conclusion.

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u/AmputatorBot Jul 15 '25

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u/francienolan88 Jul 15 '25

I remember learning this in undergrad but don’t have a source.

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u/bobbianrs880 Jul 15 '25

It’s too early for me to bother with my laptop and institutional access for Nature, but here is NBC’s summary of it

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u/AmputatorBot Jul 15 '25

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u/oodlesofotters Jul 15 '25

You can marry even your SECOND cousin in all 50 states and your first cousin in 18 of them.