What’s the Difference Between Pedigree Collapse and Endogamy?

There was current dialogue and confusion in regards to the distinction between pedigree collapse and endogamy.

Let’s check out the similarities and variations and what it means to genealogists.

Pedigree Collapse

Pedigree collapse happens when the identical individual/folks seem in your tree a number of occasions as ancestors.

On this instance, you possibly can see that John Smith and Mary Johnson seem twice, which after all means the ancestors additional again in time in these strains all seem at the very least twice too.

Genetically talking, our tester, Tester Smith, may very well be anticipated to inherit extra of the DNA of John Smith and Mary Johnson as a result of they’re receiving an infusion of their DNA from each side of their tree.

Every father or mother offers 50% of their respective DNA to every baby, however contribute totally different items of their DNA to totally different youngsters.

Every grandparent usually contributes roughly 25% to every grandchild, though it could be barely kind of. Every great-grandparent contributes about 12.5% to every great-grandchild.

Nevertheless, since John Smith seems twice in Tester Smith’s tree as a great-grandparent, John Smith can be anticipated to contribute roughly 12.5% of his DNA occasions 2 to Tester Smith. Which means roughly 25% of Tester Smith’s DNA descends from John Smith. The identical is true for John Smith’s spouse, Mary Johnson.

Let’s have a look at how this impacts our chromosomes and matching.

Chromosome Perspective with No Pedigree Collapse

First, let’s have a look at a state of affairs the place there’s no pedigree collapse. Chromosome 22 has about 72 cM of DNA that’s being in contrast for family tree, so let’s use that chromosome for our instance, with chromosome 22 being consultant of all different chromosomes (besides the X chromosome.)

If every grandparent contributes one fourth of every individual’s DNA, then our tester’s mom would have obtained roughly 25% of her DNA from her 4 grandparents, respectively, or 18 cM from every grandparent.

For functions of those examples, I’m going to make use of the 25% common quantity of DNA inherited for every grandparent, however you possibly can learn more specifics here and here, for those who’re .

On this instance with no pedigree collapse, you possibly can see that our tester obtained 9 cM or 12.5% of every of their great-grandparents’ DNA. The good-grandparents’ DNA mixed within the grandparents after which Tester’s mother and father such that Tester obtained 18 cM or 25% of their DNA from every grandparent and 9 cM or 12.5% from every great-grandparent.

Word that Tester Smith obtained one 9 cM piece of every colour of his 8 grandparents’ coloured DNA. It’s straightforward to visualise inheritance this fashion.

Chromosome Perspective with Pedigree Collapse

Our second instance reveals pedigree collapse with John Smith and Mary Johnson being current as great-grandparents twice.

Word that Tester Smith inherited a phase of John Smith’s purple DNA from their mom and one from their father. Tester additionally inherited one phase of Mary Johnson’s yellow DNA from every father or mother.

On this state of affairs, the purple DNA phase inherited by Tester Smith’s father from John Smith and the purple DNA phase inherited from Tester’s mom from John Smith might probably be:

  • The identical DNA phase contributed by John Smith to each of his youngsters, George Smith and Fred Smith, which means these segments will match solely.
  • Partially the identical DNA segments which means that a few of John Smith’s DNA that Tester Smith inherited from his mother and father will match one another and a few received’t.
  • Totally totally different DNA segments which means that though the DNA was inherited from John Smith in each circumstances, his youngsters, George Smith and Fred Smith inherited totally different items of John Smith’s DNA. That DNA was handed via George Smith and Fred Smith’s youngsters to Tester Smith. Despite the fact that each segments inherited by Tester descended from John Smith initially, they don’t match as a result of they had been totally different segments to start with.

Tester Smith will inherit roughly half of the DNA from John Smith that his mother and father obtained, so their purple segments of DNA may very well be precisely the identical, partially the identical, or utterly totally different.

Since I’m displaying the purple segments in numerous positions on the chromosomes, we’ll presume that the positions proven point out chromosome location (addresses.) For the reason that purple DNA isn’t in the identical location on the mom’s and father’s chromosomes, the DNA from John Smith inherited by Tester from his mother and father are totally different segments.

Tester can have inherited 18 cM whole from John Smith and 18 cM whole from Mary Johnson (utilizing averages). On this illustration, the purple and yellow segments, respectively are two separate 9 cM segments. If by likelihood these two purple (or yellow) segments had been inherited in adjoining areas, they might match as one 18 cM phase – regardless that they had been actually two separate segments inherited via two totally different mother and father. The phenomenon the place segments from frequent ancestors becoming a member of one another once more in descendants causes relationship predictions to be nearer than the precise relationships.

Stated one other manner, regardless that Tester Smith inherited 25% of John Smith’s DNA, John Smith continues to be a great-grandparent, albeit twice, not a grandparent regardless that distributors would predict somebody with 25% shared DNA as a grandparent.

In fact, every era additional again within the tree signifies that the quantity of DNA inherited from every ancestor is reduce in half, so the results of pedigree collapse turn out to be much less pronounced the additional again in time the collapse happens.

Taking a look at our instance, if John Smith and Mary Johnson had been duplicated in Tester’s tree one other era additional eliminated, Tester would inherit 6.25% occasions two from John Smith, or a complete of 12.5% of his DNA, and the identical from Mary Johnson. One other era again in time, 6.25% whole. Ultimately, lots of these segments will disappear solely because of loss throughout recombination, so distant pedigree collapse isn’t essentially discernable on this manner.

To summarize, pedigree collapse happens in a genealogical timeframe, which means that you possibly can at the very least probably establish the ancestors who’re duplicated in your tree. If you realize the place in your tree the duplication happens, you possibly can calculate the anticipated quantity of DNA that you’ll inherit (assuming an actual 50% inheritance/recombination fee in every era) from every of these ancestors.

Endogamy

Endogamy is totally different. As a substitute of 1 individual or a pair of ancestors who’re duplicated, testers can have no rapid ancestors who’re the identical of their tree, however they’ll have many historic ancestors who’re similar.

Endogamy most frequently happens in closed communities the place out-marriage is both extremely discouraged or inconceivable. Frequent examples embody Jewish populations, particularly in Europe with the Ashkenazi, Native Individuals, Finnish folks, Acadians, Amish, Mennonite and Brethren communities. In fact, there are various extra.

These communities typically married solely inside their very own group for a lot of generations. Every group member shares the DNA of many frequent ancestors from way back.

On this instance, the DNA from distant frequent ancestors is handed right down to the mother and father from the grandparents, however the ancestral segments are proven in small items. I used 4.5 cM because the phase dimension, however endogamous samples have many small, fragmented segments under that threshold.

“Small” segments for functions of this dialogue are these under the 6 cM minimal vendor matching/viewing threshold of FamilyTreeDNA, MyHeritage and 23andMe. Ancestry’s minimal match threshold is 8 cM. The take-away right here is that none of these particular person 4.5 cM segments would match between testers at any of these distributors as a result of they’re under all vendor’s thresholds.

The purple arrows level to small segments the place the mom and father each inherited small items of the identical similar DNA from the identical distant ancestors. Our tester will obtain the pink and purple DNA phase from each mother and father, as a result of there’s nothing else in that location for them to inherit.

The inexperienced arrows present examples of identical by chance matches the place the yellow and purple DNA, respectively, isn’t handed down from one father or mother. As a substitute, the 2 yellow and two purple segments abut and are joined to kind one 9 cM phase the place two particular person 4.5 cM segments converge – one inherited from the mom and one from the daddy.

This, after all, is the definition of similar by likelihood (IBC) the place the DNA from two mother and father simply occurs to align in such a manner that the tester matches one other individual. Nevertheless, in ADDITION to being IBC, these two smaller segments simply occurred to be from frequent earlier ancestors in an endogamous inhabitants. As a result of endogamous populations have a restricted quantity of accessible DNA, it’s way more frequent to have small segments that match in descendants – and typically recombine to match in bigger segments too.

On this case, the DNA of unknown distant ancestors simply occurred to be handed down and aligned adjoining to one another.

Our tester will match to anybody else who simply occurs to have inherited these two small ancestral DNA segments in the identical location from that very same inhabitants. When the unique variety of ancestors is restricted, so are the variety of DNA segments accessible for inheritance, and it’s quite common for random ancestral segments to align on this manner. Consider every ancestor’s tiny DNA segments salting a bowl of soup. You’re going to get some in each spoonful.

If these two adjoining 4.5 yellow segments are handed down collectively to the following era, they add as much as 9 cM, so will likely be thought of a match to a different one that inherited those self same two adjoining 4.5 cM segments from that yellow ancestor – regardless that that unknown yellow ancestor might have lived ages in the past – lengthy earlier than the opportunity of genealogical matches. When no new DNA is launched into populations, the one DNA accessible to be handed to the following era is the ancestral DNA that has been salting the identical pot of soup for generations.

That is precisely why we see the next conditions in extremely endogamous populations:

  • Many matches at decrease cM ranges because of similar by change recombination
  • Many small segments in frequent under vendor match thresholds
  • Considerably extra smaller phase matches than non-endogamous people as a result of historic ancestral DNA being handed and recombined from descendant to descendant.

A totally endogamous particular person from the Ashkenazi inhabitants typically has 4 or 5 occasions as many matches, or extra, than non-endogamous people.

Conversely, some totally endogamous people from populations that haven’t examined many individuals can have only a few matches, however could not be capable to establish their genealogical relationship with any of their matches.

Segments In contrast

Within the article Concepts – Endogamy and DNA Segments, I supplied a number of real-life examples of how endogamy impacts DNA matches.

FamilyTreeDNA’s most up-to-date matching replace, amongst different issues, has:

  • Eliminated the segments under 6 cM from the DNA match totals
  • Developed a brand new method to find out and take away many similar by likelihood (IBC) matches
  • Absolutely imputed all switch kits from different distributors (yay!,) which means that early transfers who didn’t beforehand have distant matches now do
  • Recalculated everybody’s matches based mostly on all the above
  • Developed an improved relationship prediction algorithm
  • Re-predicted everybody’s relationships

Whereas these modifications profit everybody, they supply big advantages to folks with excessive numbers of matches because of endogamy.

On this chart from the sooner article, you possibly can see people predicted to the identical relationship stage, with segments as small as 1 cM displaying, though matching by no means occurred at this stage:

  • Non-endogamous matches at left
  • Jewish matches within the middle
  • Native American matches at proper.

The chromosomes of the Jewish and Native folks look polka dotted by comparability to the non-endogamous folks. All of their matching segments are shorter then the non-endogamous group on the similar predicted stage, as a result of all the small segments had been included within the relationship prediction calculations.

The removing of segments under 6 cM at FamilyTreeDNA improves accuracy and relationship predictions for everybody. A white paper will likely be accessible quickly describing their new methods.

Inhabitants Genetics

Whereas endogamous matches are irritating for genealogists because of each the excessive variety of matches and the problem figuring out frequent pedigree ancestors, endogamous matches are very helpful in one other manner.

Taking a look at our endogamous instance once more, let’s say our tester is solely Jewish, with no admixture.

Our tester has a toddler with a companion who’s solely Asian, with no admixture. The DNA of those two populations doesn’t match the identical genetic sample.

On this instance, the Asian individual’s DNA is chartreuse inexperienced (for simplicity.) The Jewish DNA within the baby has been divided in half, shedding all the military inexperienced, shiny blue, and light-weight blue segments, together with a part of the tan, gray and yellow segments. Discover that the kid nonetheless has two yellow segments and two purple ones.

Inhabitants geneticists search for distinct patterns amongst populations of people that have lived solely collectively, in shut proximity, or combined typically for tell-tale genetic alerts the place excessive frequencies of sure DNA patterns, or colours right here, seem. Consider an island like Australia or New Zealand the place there have been no new populations accessible.

These telltale small DNA segments, under matching thresholds, sign membership in or a genetic affiliation with that inhabitants. In fact, not all populations are fairly as distinctive because the Jewish or Aussie/NZ populations. Some populations haven’t been remoted as lengthy or extra admixture has taken place. Take into consideration Europe and those fluid borders.

Nonetheless, the sign of the founding populations is current for a number of generations, and typically longer if the testers ancestors had been from the identical inhabitants or area of the world and people figuring out segments have been preserved throughout genetic recombination.

This particular person’s ethnicity or populations would doubtless be predicted at or close to 50% Jewish and 50% Asian. These populations have been separated for tens of hundreds of years and are comparatively straightforward, genetically, to inform aside.

Nevertheless, ascertaining between France and Germany is one other matter altogether.

Actual Life Examples

Within the “image is price a thousand phrases” class, let’s check out some visuals.

Genetic Affairs has developed autocluster know-how which I’ve written about several times. Within the introductory article AutoClustering by Genetic Affairs, I supplied examples of “regular” non-endogamous autoclusters.

A non-endogamous particular person the place different folks from their household strains have examined would present a number of separate clusters. People included in the identical coloured cluster match one another. These clusters signify totally different ancestors or ancestral {couples}. For essentially the most half, the folks in particular person clusters don’t match different clusters, though some will because the smaller clusters are likely to signify generations additional again in time. The individuals who match two clusters are proven by gray cells.

However, individuals who descend from a wholly endogamous inhabitants just about have one massive interrelated sq., not neatly organized descending coloured blocks.

My mom’s great-grandfather is Acadian, a extremely endogamous inhabitants. She has no recognized pedigree collapse outdoors of the Acadian inhabitants. Nevertheless, the Acadian inhabitants has substantial pedigree collapse which means that almost all of her matches would have substantial pedigree collapse. All Acadians share the identical founding ancestors from the early 1600s.

As researchers, we’re lucky to have meticulous Catholic church and tax data maintained by the Acadians. Different genealogists aren’t almost as lucky and subsequently can’t essentially differentiate between endogamy and pedigree collapse or a mix of each.

Mom would have inherited about 12.5% of her DNA from Antoine (Anthony Lord) Lore.

Mother’s orange Acadian cluster at higher left is outsized, a lot bigger than her subsequent cluster, and you’ll see that many orange-cluster individuals are associated to one another. Mother has extra Acadian matches than would usually account for 12.5% of her matches on the threshold used to generate the autocluster. These proportionally outsized autoclusters are the hallmark of endogamy.

One era additional downstream, my Acadian cluster, which accounts for six.25% of my DNA continues to be my largest cluster, proven under, NOT clusters from my 4 grandparents as may be anticipated.

Nevertheless, my Acadian cluster isn’t almost as massive as my mom’s, illustrating simply how a lot was misplaced via recombination in a single era.

My pal and professional Dutch genealogist, Yvette Hoitink was gracious sufficient to supply an instance of endogamy from a person whose ancestors had been from Winterswijk, a small village within the Netherlands.

Graphic courtesy of Yvette Hoitink

Yvette tells us that in Winterswijk, folks had been serfs, some till 1795, and had been required to pay a advantageous in the event that they married a serf belonging to a unique landlord.

Now, along with being a small village, we perceive why so many individuals had been associated to one another, and why the opposite clusters are so tiny. Do observe that lots of the folks within the purple cluster additionally match folks within the different coloured clusters too, as recognized by the gray cells. Actually, everybody does appear to be associated to (at the very least) a few of this individual’s different ancestors.

Courtesy Yvette Hoitink

Simply so that you don’t suppose all Dutch individuals are endogamous, Yvette additionally supplied this autocluster of a person from Friesland the place folks weren’t serfs throughout that timeframe.

Regional variations and inhabitants historical past, each on a big or small scale, actually do make a HUGE distinction.

Pedigree Collapse, Endogamy and Their Cousin, Inhabitants Genetics

I hope you’ve gotten a greater thought how pedigree collapse is totally different than endogamy and why endogamy is helpful in inhabitants genetics.

  • Pedigree collapse means you’ve gotten the identical ancestor(s) current in your tree, however apart from these strains, it does NOT imply that everybody in your tree is said to one another.
  • When everybody inside a gaggle is said in some way to everybody else, that’s endogamy.
  • In fact, like many issues in life, these “states of being” usually are not unique and completely separate. You possibly can have pedigree collapse with out endogamy, however long-term group pedigree collapse inside a gaggle of individuals, such because the Acadians, defines endogamy.
  • When endogamy is current, actually everyone seems to be in some way associated to everybody else, a technique or one other – particularly distantly.
  • You possibly can have endogamy with none recognized current ancestors.
  • It’s also possible to have each pedigree collapse and endogamy, collectively, like my Acadian household line. In case you do, I’m sorry😊!

With pedigree collapse, you’ve gotten duplicate ancestors however you realize who they’re.

With endogamy, you’ll have an enormous distant household, but it surely’s tough or typically inconceivable to find out which ancestors, even for those who DO know who they’re, contributed particular DNA segments. Numerous matches with smaller matching DNA segments are prevalent and certain end result from distant population-based matches.

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