# Are cousins with twin parents genetic siblings? **URL:** \ **Category:** Factual Questions\ **Created:** [August 15, 2020, 2:07am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146 "2020-08-15T02:07:53Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 15, 2020, 6:03pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/21 "2020-08-15T18:03:29Z")
> [@RivkahChaya](#): > > I doubt they will fingerprint the babies at birth, I should have said footprints instead of fingerprints. According to this, about [90% of hospitals take infant footprints at birth](https://www.uchealth.org/today/electronic-scans-of-newborn-footprints-add-another-line-of-security/) and also take the mother’s fingerprints. The practice started in the 1960s with ink and paper prints but now can be done by electronic scans. ---
**Author:** ![CairoCarol](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cairocarol/32/3825_2.png) [@CairoCarol](https://boards.straightdope.com/u/CairoCarol)\ **Post date:** [August 15, 2020, 7:07pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/22 "2020-08-15T19:07:17Z")
Another way in which a mix-up may be easily avoided is if they give birth on different days, especially if the births are a week or more apart. I looked at the article to see if there was a mention of due dates - there was not, although the article did say that the couples deliberately tried to get pregnant at the same time. Speaking of the article, does anyone else get a faintly opportunistic whiff from this family? It looks to me like they are strongly selling the double-twin angle, in hopes of getting a reality TV show perhaps, or at the very least “Gerber donates 1 year of baby food for each child!” sort of publicity. I mean, they may be perfectly nice people, but the whole thing kind of put me off. ---
**Author:** ![Wheelz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wheelz/32/5718_2.png) [@Wheelz](https://boards.straightdope.com/u/Wheelz)\ **Post date:** [August 15, 2020, 8:09pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/23 "2020-08-15T20:09:17Z")
> [@CairoCarol](#): > > Speaking of the article, does anyone else get a faintly opportunistic whiff from this family? It looks to me like they are strongly selling the double-twin angle, in hopes of getting a reality TV show perhaps, or at the very least “Gerber donates 1 year of baby food for each child!” sort of publicity. I mean, they may be perfectly nice people, but the whole thing kind of put me off. I agree. And, twins or not, isn’t it a bit weird for an adult married couple to live with another adult married couple? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [August 15, 2020, 8:26pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/24 "2020-08-15T20:26:40Z")
They call it “performative parenting”, right? More hashtags than content in their Instagram post is a bit of a red flag. But at least their situation is somewhat interesting. I’d rather watch their reality show than the Kardashians. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [August 15, 2020, 8:28pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/25 "2020-08-15T20:28:55Z")
> [@CairoCarol](#): > > Speaking of the article, does anyone else get a faintly opportunistic whiff from this family? It looks to me like they are strongly selling the double-twin angle, in hopes of getting a reality TV show perhaps, or at the very least “Gerber donates 1 year of baby food for each child!” sort of publicity. I mean, they may be perfectly nice people, but the whole thing kind of put me off. The Fox News article in the OP mentions there was already a TLC special and they have a joint Instagram page so they’re already selling themselves. (And if you’re wiser than I am, you’ll avoid reading the comments on that article.) ---
**Author:** ![Baker](https://avatars.discourse-cdn.com/v4/letter/b/bb73d2/32.png) [@Baker](https://boards.straightdope.com/u/Baker)\ **Post date:** [August 15, 2020, 8:36pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/26 "2020-08-15T20:36:14Z")
I used to shop at a small grocery store run by two couples, identical brothers married to identical sisters. They even lived in a shared duplex they built. I saw some of their adult children and they sure looked a lot alike too, but they were just double cousins who shared a close genetic pattern. My materal grandmother had double cousins, as in her parents generation two brothers and a sister in one family married to sisters and a brother in another. No identicals were involved there. And just to show how old I am I remember an episode of I’ve Got A Secret in which the secret was that a set of identical triplet men married a set of identical triplet women. ---
**Author:** ![lobotomyboy63](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobotomyboy63/32/2900_2.png) [@lobotomyboy63](https://boards.straightdope.com/u/lobotomyboy63)\ **Post date:** [August 15, 2020, 9:15pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/27 "2020-08-15T21:15:42Z")
> [@Baker](#): > > And just to show how old I am I remember an episode of I’ve Got A Secret in which the secret was that a set of identical triplet men married a set of identical triplet women. I never saw it, but thought identical triplets has to be rare. Googling… > [@](#): > > A 2012 case report of a healthy set of three identical triplet boys conceived spontaneously lists the incidence at 1 in 100,000 live births, with most of the reported cases conceived through assisted reproductive techniques.1 > **[How Triplets Can Be Identical](https://www.verywellfamily.com/identical-triplets-2447414)** > > Triplets can be identical (monozygotic), but it is very rare. More commonly, two eggs are fertilized and then one splits, resulting in triplets. As far as the OP goes, here’s a chart showing various fractions of relatedness. Parent vs. sibling vs. your child: all equally related to you, 1/2. First cousins would be 1/8…double first cousins 1/4… What if (for instance) both fathers were identical twins but the mothers were non-twin sisters? It would be more than 1/4 but less than half. Would they have 3/8 of their genes in common? [https://images.app.goo.gl/oWMWKg3NqLCo9Ce69](https://images.app.goo.gl/oWMWKg3NqLCo9Ce69) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 15, 2020, 10:14pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/28 "2020-08-15T22:14:55Z")
> [@Riemann](#): > > The author of the article is quoting a tweet by the parents. Informally, it’s obvious what they meant, probably based on a mangled understanding of genetic terminology. But it’s not correct, and it’s certainly not the terminology a geneticist would use. Your degree of genetic identity by descent does not define your familial relationship to someone. Even without this highly unusual familial situation with two pairs of identical twins, it’s entirely possible for cousins to have 50% i.b.d. through inbreeding. This would not magically make such cousins into siblings, they are still inbred cousins. Also, of course, there is no one-to-one mapping between familial relationship and degree of i.b.d. Yes, being “siblings” is more than just a matter of degree of relatedness, as evidenced by your inbreeding example: The genetic comparison between a pair of inbred cousins is very different from the comparison between a pair of normal siblings. But in this case, the children do have exactly the same genetic relationship as if they were siblings. And “genetic siblings” is a perfectly reasonable shortened term for “people who have exactly the same genetic relationship as siblings”. ---
**Author:** ![Baker](https://avatars.discourse-cdn.com/v4/letter/b/bb73d2/32.png) [@Baker](https://boards.straightdope.com/u/Baker)\ **Post date:** [August 15, 2020, 10:25pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/29 "2020-08-15T22:25:40Z")
You know what’s even more rare, is identical quadruplets. They do happen. I watched a program on multiple births, and a young couple had a set of identical quad boys. She got annoyed when folks kept asking if fertility drugs had been used, and she’d have to tell them identical births did not come from drugs. Not so long after I saw the same boys in a Tide commercial. Check out this Google link to stories about identical quads. [https://www.google.com/search?sxsrf=ALeKk030txDxlLhG4RCjDMZaKaj72Vs1pw%3A1597530171424&source=hp&ei=O2A4X7H5FpGIsQXb-Y2YDA&q=identical+quadruplets&oq=identical+&gs\_lcp=CgZwc3ktYWIQARgFMgUIABCxAzIFCAAQsQMyBQguELEDMgUIABCxAzIICAAQsQMQgwEyAggAMgIIADICCAAyAggAMgIIADoECCMQJzoLCC4QxwEQrwEQkQI6BQgAEJECOg4ILhCxAxCDARDHARCjAjoLCC4QsQMQxwEQowI6CAgAELEDEJECOg0ILhDHARCvARAUEIcCOggILhCxAxCDAToICC4QsQMQkwI6BwgAEBQQhwI6CgguEMcBEK8BEAo6CAguEMcBEK8BUKIHWNojYNdFaABwAHgAgAGkAYgB8AiSAQMyLjiYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab](https://www.google.com/search?sxsrf=ALeKk030txDxlLhG4RCjDMZaKaj72Vs1pw%3A1597530171424&source=hp&ei=O2A4X7H5FpGIsQXb-Y2YDA&q=identical+quadruplets&oq=identical+&gs_lcp=CgZwc3ktYWIQARgFMgUIABCxAzIFCAAQsQMyBQguELEDMgUIABCxAzIICAAQsQMQgwEyAggAMgIIADICCAAyAggAMgIIADoECCMQJzoLCC4QxwEQrwEQkQI6BQgAEJECOg4ILhCxAxCDARDHARCjAjoLCC4QsQMQxwEQowI6CAgAELEDEJECOg0ILhDHARCvARAUEIcCOggILhCxAxCDAToICC4QsQMQkwI6BwgAEBQQhwI6CgguEMcBEK8BEAo6CAguEMcBEK8BUKIHWNojYNdFaABwAHgAgAGkAYgB8AiSAQMyLjiYAQCgAQGqAQdnd3Mtd2l6&sclient=psy-ab) ---
**Author:** ![doreen](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@doreen](https://boards.straightdope.com/u/doreen)\ **Post date:** [August 15, 2020, 11:44pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/30 "2020-08-15T23:44:10Z")
That depends on exactly what they mean by “live in the same home”. if they mean it’s a single family house, it’s a little weird. If they mean there are two separate apartments and they don’t lock the apartment doors, it’s not unusual in my experience when both apartments are occupied by relatives. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [August 16, 2020, 1:41am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/31 "2020-08-16T01:41:47Z")
If twins marry twins then living in the same home doesn’t seem that weird to me. I had relatives that shared a house with an unrelated family for economic reasons. It was out of the ordinary but there are plenty of extended family living situations, after a while it didn’t seem any different than that. ETA; I should mention another example, I had neighbors where the wife had a twin sister. Her sister and brother-in-law were over at their house all the time. They didn’t live there but they were just as much neighbors to me because I saw them so often. ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [August 16, 2020, 3:08am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/32 "2020-08-16T03:08:38Z")
> [@lobotomyboy63](#): > > First cousins would be 1/8…double first cousins 1/4… What if (for instance) both fathers were identical twins but the mothers were non-twin sisters? It would be more than 1/4 but less than half. Would they have 3/8 of their genes in common? All of the numbers in that chart are averages, except for .5 for the relationship between parent and child. Children always get half of their genes from one parent, and half from the other (excluding chromosomal abnormalities, and ignoring sex chromosomes, mitochondria, and chloroplasts). Identical twins having children with a pair of siblings would result in the children being in between half-sibs and full-sibs. In your example the children have the “same” father, but two different mothers (so normal half-sibs, related on average .25), but the mothers happen to be sisters, so that brings another .125 to the party, so they would be half-sibs and a half or something at .375. Those distributions around the averages are pretty important, and extremely obvious when looking at the relationship data for lots of families graphed together. Putative siblings will make a curve centered on .5, but there will be tails and outliers on both ends (cousins raised as sibs? fraternal cuckoldry? inbreeding in the parents? random chance?) ---
**Author:** ![lobotomyboy63](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobotomyboy63/32/2900_2.png) [@lobotomyboy63](https://boards.straightdope.com/u/lobotomyboy63)\ **Post date:** [August 16, 2020, 3:32am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/33 "2020-08-16T03:32:26Z")
> [@echoreply](#): > > Identical twins having children with a pair of siblings would result in the children being in between half-sibs and full-sibs. In your example the children have the “same” father, but two different mothers (so normal half-sibs, related on average .25), but the mothers happen to be sisters, so that brings another .125 to the party, so they would be half-sibs and a half or something at .375. OK, thanks, it is as I thought. > [@Baker](#): > > You know what’s even more rare, is identical quadruplets. One egg gets fertilized and splits, giving twins. Split again, quads. But how to get to triplets? The identical triplets article suggests that sometimes they began as identical quadruplets and one was absorbed. Years ago I saw a thing on TV about a woman who needed a kidney (?) transplant and the doctors said to bring in willing relatives to see if they could find a good match. Her sons came and the doctors came back and said, “Um, this is odd, but this son…well, he’s not your son.” She said, “I was there…he’s mine.” Short story long, it turned out she was a chimera. At some point in her development as an embryo, the cell line diverged into two and multiplied forth from there. So when they tested her blood’s DNA they got one signature. But when they tested another cell line (her liver’s, maybe?), they got a different signature. So according to one DNA test she wasn’t the mother…according to another, she was. Fascinating stuff. ---
**Author:** ![Baker](https://avatars.discourse-cdn.com/v4/letter/b/bb73d2/32.png) [@Baker](https://boards.straightdope.com/u/Baker)\ **Post date:** [August 16, 2020, 4:14am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/34 "2020-08-16T04:14:37Z")
I saw a show about conjoined twins being seperated. The young girls were from Thailand. There was a third sibling identical to them. The egg must have split once, then on started agaiin to split but did not complete the process. And speaking of identical marrying ordinary siblings, there were Chang and Eng Bunker, who gave the name “Siamese” to conjoined twins. They settled down in North Carolina and married two women who were regular sisters. Imagine that wedding night. After their families grew large they built a second house, and spent three days at a time in each, going back and forth. One fathered twelve kids and the other had ten. ---
**Author:** ![Temporary\_Name](https://avatars.discourse-cdn.com/v4/letter/t/8c91f0/32.png) [@Temporary\_Name](https://boards.straightdope.com/u/Temporary_Name)\ **Post date:** [August 16, 2020, 4:20am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/35 "2020-08-16T04:20:37Z")
> [@Broomstick](#): > > Double first cousins will share more genes in common than non-double-first cousins - that’s genes both good and bad. Assuming no identical twins involved, siblings will always be more closely related than cousins. > > While [Charles II of Spain](https://en.wikipedia.org/wiki/Charles_II_of_Spain) is often held up as an example of why too many first-cousin marriages are bad his full sister [Margaret Theresa](https://en.wikipedia.org/wiki/Margaret_Theresa_of_Spain) is proof that an incestuous background does not always impose calamity. But the Spanish Hapsburgs had an unusually straight family ~~tree~~ pole with startlingly few branches. Outside of royalty, such inbreeding in humans is very rare. Actually, inbreeding to that degree is pretty rare even among royalty. As the Hapsburgs demonstrated (as did a few Ancient Egyptian dynasties) after a few generations fertility drops off significantly. There are conceptions but few live births or long-surviving infants and if the family persists in that form of mating eventually you get no offspring at all. I recently heard a podcast where a former Mormon claimed that along the Arizona Utah border where polygamist marriages are common and inbreeding is very common, that the women often give birth to what he described as a cell mass of protoplasm. (If I am remembering his terminology correctly.) I was pretty dismissive of that claim, but might it be true in light of the quoted post? (Unrelated to this discussion but curious if true, he also claimed they prayed for and hoped for disabled kids because they are often docile and easy to attend to – plus they get extra money from the government. Apparently the entire community relies upon government assistance to survive.) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 16, 2020, 5:19am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/36 "2020-08-16T05:19:41Z")
> [@Temporary\_Name](#): > > I was pretty dismissive of that claim, but might it be true in light of the quoted post? It’s purest bullshit. I don’t even know what a “cell mass of protoplasm” is supposed to mean. Inbreeding could result in miscarriages, but a “cell mass” would be at a such an early stage of pregnancy that it might not even be recognized as a miscarriage. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [August 16, 2020, 5:27am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/37 "2020-08-16T05:27:42Z")
I just hope the “genetic siblings” have this all explained to them before they check their 23andme account. I’d be a little freaked out if I saw one of my cousins listed as a sibling. ---
**Author:** ![needscoffee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/needscoffee/32/1076_2.png) [@needscoffee](https://boards.straightdope.com/u/needscoffee)\ **Post date:** [August 16, 2020, 5:30am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/38 "2020-08-16T05:30:45Z")
> [@Temporary\_Name](#): > > he also claimed they prayed for and hoped for disabled kids because they are often docile and easy to attend to This also sounds like bs. More often, a disabled child will require extra individual attention. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [August 16, 2020, 7:59am UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/39 "2020-08-16T07:59:38Z")
> [@Temporary\_Name](#): > > (Unrelated to this discussion but curious if true, he also claimed they prayed for and hoped for disabled kids because they are often docile and easy to attend to – plus they get extra money from the government. Apparently the entire community relies upon government assistance to survive.) Anyone who thinks disabled kids are “easy to attend to” has never changed the diaper on an adult-sized human being. As for the government dependency - yes, to a large extent that’s true. The lucky few men who get to marry [(as opposed to being literally abandoned along a highway when late teen/young adult)](https://en.wikipedia.org/wiki/Lost_boys_(Mormon_fundamentalism)) can only legally marry one wife - the rest are married in their church but are legally single and thus quality for aid as such. So all those virile, manly men screw multiple women and have them pumping out babies without having to actually, you know, _support_ those women and kids like in most other cultures allowing polygamy. The FLDS _do_ have a high rate of birth defects, including the world’s only cluster of [fumarase deficiency](https://en.wikipedia.org/wiki/Fumarase_deficiency). > [@needscoffee](#): > > This also sounds like bs. More often, a disabled child will require extra individual attention. The men in those communities might believe such, as such children will be quiet and not rebellious, both qualities those in charge try to cultivate. The men in charge will not be the ones changing the diapers or trying to lift older/adult children into and out of wheelchairs. ---
**Author:** ![doreen](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@doreen](https://boards.straightdope.com/u/doreen)\ **Post date:** [August 16, 2020, 12:44pm UTC](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146/40 "2020-08-16T12:44:20Z")
> [@Broomstick](#): > > Anyone who thinks disabled kids are “easy to attend to” has never changed the diaper on an adult-sized human being. > [@Broomstick](#): > > The men in charge will not be the ones changing the diapers or trying to lift older/adult children into and out of wheelchairs. That’s true- but that’s not the sort of disability they’re hoping for. SSI isn’t only for people with physical disabilities - people with intellectual disabilities also qualify. I have a couple of relatives who began receiving SSI as adults\* who don’t require any physical care at all - but they will never be able to live independently. When their parents die, they will either have to move in with one their siblings or into a group home. - SSI is means-tested, and for children it will depend on their parents’ income. [Previous page](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146.md?page=1) [Next page](https://boards.straightdope.com/t/are-cousins-with-twin-parents-genetic-siblings/918146.md?page=3)