In genetics, a mosaic (or mosaicism) means the presence of two different genotypes in an individual which developed from a single fertilized egg. As a result, the individual has two or more genetically different cell lines derived from a single zygote.[1]

Mosaicism may result from:

The phenomenon was discovered by Curt Stern. In 1936, he demonstrated that recombination, normal in meiosis, can also take place in mitosis.[2] When it does, it results in somatic (body) mosaics. These are organisms which contain two or more genetically distinct types of tissue.[3]

A genetic chimera is an organism composed of two or more sets of genetically distinct cells. Dispermic chimeras happen when two fertilized eggs fuse together. Mosaics are a different kind of chimerism: they originate from a single fertilized egg.

This is easiest to see with eye colours. When eye colours vary between the two eyes, or within one or both eyes, the condition is called heterochromia iridis (= 'different coloured iris'). It can have many different causes, both genetic and accidental. For example, David Bowie had the appearance of different eye colours due to an injury that caused one pupil to be permanently dilated.

On this page, only genetic mosaicism is discussed.

The most common cause of mosaicism in mammalian females is X-inactivation. Females have two X chromosomes (and males have only one). The two X chromosomes in a female are rarely identical. They have the same genes, but at some loci (positions) they may have different alleles (versions of the same gene).

In the early embryo, each cell independently and randomly inactivates one copy of the X chromosome.[4] This inactivation lasts the lifetime of the cell, and all the descendants of the cell inactivate that same chromosome.

This phenomenon shows in the colouration of calico cats and tortoiseshell cats. These females are heterozygous for the X-linked colour genes: the genes for their coat colours are carried on the X chromosome. X-inactivation causes groups of cells to carry either one or the other X-chromosome in an active state.[5]

X-inactivation is reversed in the female germline, so that all egg cells contain an active X chromosome.

Mosaicism refers to differences in the genotype of various cell populations in the same individual, but X-inactivation is an epigenetic change, a switching off of genes on one chromosome. It is not a change in the genotype.[6] Descendent cells of the embryo carry the same X-inactivation as the original cells. This may give rise to mild symptoms in female 'carriers' of X-linked genetic disorders.[7]

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Mosaic (genetics) - Simple English Wikipedia, the free ...

Why is it that some species seem to be particularly attentive parents while others leave their young to fend for themselves? For years, scientists have believed one of the major drivers is experience an animal raised by an attentive parent, the argument goes, is likely to be an attentive parent itself.

A Harvard study is challenging that idea, and breaking new ground by uncovering links between the activity of specific genes and parenting differences across species.

Led by Professor of Organismic and Evolutionary Biology and Molecular and Cellular Biology Hopi Hoekstra and postdoctoral researcher Andrs Bendesky, the study found not only that different genes may influence behaviors in males and females, but also that the gene for the hormone vasopressin appears to be closely tied to nest-building behavior in parenting mice. The research is described in an April 19 paper published in Nature.

This is one of the first cases in which a gene has been implicated in parental care in a mammal, Hoekstra said. In fact, its one of the few genes that has been implicated in the evolution of behavior in general but what I think is particularly exciting about this is the idea that, while in many systems we know that parenting behavior can be affected by your environment, we now have evidence that genetics can play an important role as well.

We know there is variation between species in how much parental behavior they provide for their young, Bendesky said. Its not that one is better or worse, theyre just different strategies but before our study we had no idea how these parental behaviors evolved, whether there was one gene that mediates all of the differences in behavior, or if it was 10 or 20.

The idea for the study grew out of differences in mating systems researchers had observed between two sister mouse species Peromyscus maniculatus, also known as the deer mouse, and P. polionotus, the oldfield mouse.

Like many rodents, the deer mouse is what we refer to as promiscuous, meaning both males and females mate with multiple individuals, Hoekstra said. Often when you genotype a litter, you will find pups from multiple fathers.

The oldfield mouse, by comparison, is monogamous, so all the pups in a litter are sired by one father.

Its been widely documented that these mice have different mating systems, Hoekstra said. When Andrs joined the lab, he was interested in asking the question: Do those differences translate into differences in parental care?

Bendesky first created a behavioral assay that tracked the behavior of males and females of each species and measured how often they engaged in parental behavior such as building nests and licking and huddling their pups.

In general, the data showed that females of both species were attentive mothers. The major differences, Hoekstra said, were in the fathers. Oldfield mice fathers were as involved in raising pups as oldfield mothers, but deer mice fathers werent.

To test the impact of different parenting styles, Bendesky performed a cross-fostering experiment, allowing oldfield mice parents to raise deer mouse pups, and vice versa. The researchers then observed the parenting behavior of the pups when they became parents themselves.

What we found was theres no measurable effect based on who raises them, Hoekstra said. Its all about who they are genetically.

To investigate those genetics, the researchers crossbred the species, then crossbred the offspring, creating second-generation hybrid mice that had regions of the genome from each species.

When the team began to identify regions in the genome that were associated with behavioral differences between the species, they discovered that some effects were sex-specific, but that some regions appeared to influence a handful of behaviors.

By Peter Reuell, Harvard Staff Writer | November 17, 2016 | Editor's Pick

What I find very interesting is that we found different genes may explain the evolution of paternal and maternal care, Bendesky said. Thats interesting because it tells us that if some mutation in a population increases maternal care, it may not affect the behavior of males. So these behaviors may be evolving independently.

The other significant result here is that there are some regions that affect multiple traits, and others that have very specific effects, Hoekstra added. For example, we found one region that affects licking, huddling, handling, and retrieving, but another that affected only nest-building.

Bendesky turned to locating individual genes that might be linked with parental behaviors.

We looked at expression in a region of the brain called the hypothalamus, which is known to be important in social behavior, Hoekstra said. Specifically, we were looking at which genes showed differences in expression between the two species. While each region might contain hundreds of candidate genes, there were only a handful that fit those criteria.

Almost immediately, she said, one gene for the production of vasopressin, part of a pathway past findings had linked to social behavior in voles jumped out at them.

To test whether vasopressin affected parental behavior, Bendesky administered doses of the hormone to male and female oldfield mice, and found that nest-building behavior in both dropped. A similar experiment in collaboration with Catherine Dulacs lab, which used genetic tools to manipulate the activity of vasopressin neurons in lab mice, confirmed these results.

The findings also open the door to new insight on the neurological circuitry involved in parental behavior.

This gives us molecular handles to start understanding the circuitry much better, Bendesky said. We can see what is happening in the brain not in the abstract but we can say vasopressin is going from this part of the hypothalamus to this other part of the brain, so we can see how the brain is organized.

By Jill Radsken, Harvard Staff Writer | April 20, 2017

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Harvard team leads breakthrough on the genetics of parenting - Harvard Gazette

Atrial fibrillation is a heart disorder that causes the upper chambers of the heart to spasm instead of beating regularly. While that sounds dangerous, the lack of a regular heartbeat itself isn't dangerous. Instead, a-fib causes lots of indirect problems that can be debilitating or fatal. We're making progress in understanding the disease, as evidenced by two new papers that identify a total of 18 genes that predispose people to a-fib.

That should be exciting news. And it should be especially exciting to me, since I could have easily contributed to that studyas one of its subjects. I have a-fib, which I seem to have inherited from my mother.

Getting a better understanding of a disease can open all sorts of possibilities for better treatments, even ones tailored to your own particular genetics. But that's not really the case with a-fib, and it provides a great example of how science can sometimes run up against limits even as it successfully increases our knowledge.

Your heart has four chambers, two smaller ones on top called atria, and two much larger ones called ventricles. The rhythmic beat of your heart is the product of the regular contractions of these sets of chambers, first the atria, and then the ventricles. These contractions are organized by the unique properties of the heart muscle cells. These cells are driven to contract by a small electrical jolt delivered by a neighboring cell. In addition to contracting, this jolt causes these cells to release ions from storage areas, creating a small electrical jolt that they forward to their neighbors.

Some of their neighbors have already contracted, and so can't respond to this electrical signal immediately. The rest contract and forward it on further. This creates a wave of contractions that can only travel in one direction: away from the source of the signal at the top of the atria (or top of the ventricles), towards cells that haven't yet been triggered to contract. This organized wave of contraction, combined with a system of valves, drives the flow of blood in one direction.

In a-fib, all of this goes wrong. Multiple signals start, and take confused routes through the heart. Rather than a directional wave of contraction, the atria twitch and spasm. Rather than being driven in to the ventricles, the blood gets pulled in irregularly as they expand.

This might sound catastrophic, but the main force driving your blood through your body is the contraction of the larger ventricles. Some people remain completely unaware that they've developed a-fib until it's picked up during routine screening. Others, however, experience a variety of symptoms: pounding or irregular heart beats, changes in blood pressure, light headedness, and more. (My a-fib announced itself by a racing, pounding heartbeat that woke me from sleep at two in the morning.)

But none of those symptoms makes a-fib a serious health threat. Instead, the problems are invisible and insidious. Without the ordered contractions that drive blood out of the atria, it tends to pool up in the quieter corners, sometimes forming small clots. These eventually travel throughout the body until they lodge in small blood vessels, cutting off the blood supply to a small piece of tissue. Over time, this damage piles upin the heart, in the brain. A-fib is a major risk factor for strokes, heart failure, and early-onset dementia.

It's a terrible disease for those who suffer from these debilitating consequences, and they place a large burden on our healthcare system. Obviously, understanding more about why it happens would be a positive development.

Some cases of a-fib are rare events, brought on by things like hormone imbalances or even a bout of heavy drinking (ER doctors apparently refer to it as "Friday night heart"). But for many people, once it starts, it's there to stay. And it tends to run in some families like mine, suggesting that genes can help contribute to the risk of developing the disorder.

That fact would seem to provide a lot of hope for people suffering from it. After all, if we could understand the gene involved, we might be able to identify the environmental factors that convert that risk into actual symptoms. Or we could design drugs that specifically target the defective proteins that are causing the problem. Or even, in the not too distant future, we could intervene at the genetic level itself, editing or replacing the troublemaking stretch of DNA.

Genetics, as these new papers drive home, isn't being quite so cooperative. There is not a single, or even a handful of genes involved in raising the risk of a-fib; the new papers bring the total up to the neighborhood of 30, with the potential for even more to come. Some risk factors appear for the moment to be specific to different ethnic groups, for reasons we don't understand yet.

And, perhaps most significantly, they show that, on a biological level, a-fib isn't a single disorder. It's four or more. Many of the genes encode channels that let ions move within and between cells, an activity that helps create the tiny electrical jolts that trigger contractions. Others seem to be involved in the structure of cardiac muscle itself. Yet another class appears to help control the development of the heart, and may cause the disorder by creating structural defects. A possibly related class helps the nervous system form connections; failure of that process could also lead to structural defects.

Then there are the oddballs that we don't understand at all yet, like the genethat is involved in a-fib and "has been shown to be important in determining the invasiveness of cancer cells and has been suggested to mediate the neurotoxic effect of -amyloid in Alzheimer disease."

It's easiest to see why these results are pretty unhelpful by going through different points where you could intervene with a-fib. For most people, a-fib doesn't develop until later in life (mine started in my 40s), suggesting that it might involve some combination of genetic predisposition and environmental factors. But the complicated genetics suggest that, if environmental factorsexist, there may be lots of them, some specific to different classes of genes. It's a recipe for incredibly slow progress; teasing out any one of these could potentially take an entire career, and numerous (and expensive) human cohort studies.

Another option for intervention, and one used now, is to minimize the consequences of a-fib. The worst of these are caused by blood clots, so people with the disorder are often given anti-coagulants. (The recent development of a more effective anticoagulant has even led to an a-fib-specific pharmaceutical ad blitz.) Here, the underlying genetics are irrelevant. Regardless of what's causing the disease, limiting the risk of blood clots will be effective at cutting down on consequences.

For some of the genes, however, there is some cause for optimism when it comes to other treatments. Standard therapiesfor a-fib include trying a set of drugs that tone down the action of ion channels, making the heart a bit less reactive to electrical signals. This can reduce or eliminate periods of a-fib for some people, but finding the right drug and dose is a matter of trial and errorone that doesn't always end in success. If we know that a specific ion channel is the problem in a patient, it's possible that we could direct this process with some intelligence, identifying those who a drug is likely to work for and which drugs are likely to work.

But for people with structural defects put in place early in development, the only option would seem to be to redo the architecture of the heart. And, perhaps surprisingly, this is an option. But it doesn't depend on knowing anything about the heart's architectural problems.

The standard surgical intervention for a-fib relies on a somewhat odd finding. Medical researchers noted that cardiac muscle cells don't stay restricted to the heart. A few of them will migrate up into the blood vessels that connect the atria to the lungs. There, they end up outside the flow of electrical signals that organizecontractions across the heart. But, if they happen to contract spontaneouslysomething heart muscle cells will do even if you're growing them in culture dishthey can send electrical signals back in to the heart. These signals can interfere with the heart's normal rhythm, setting off a-fib.

The surgical treatment involves sending a probe through arteries and into the heart. There, doctors use an intense burst of radio waves to heat and kill small groups of cardiac cells, burning rings around the blood vessels that lead to the lung. These rings are repaired by scar tissue, which doesn't conduct electrical signals. Thisworks in the majority, but not all casessome people need try it multiple times before their a-fib is calmed. If the procedure is successful, though, the cells in the blood vessels can send all thesignals they want towards the atria;they never get there. Freed of the interference, the heart beats normally.

Perhaps the most striking thing about this procedure is that it seems to work for nearly everyone, regardless of what type of genetic predisposition they might have. For people who end up opting for this treatment, their genetic status is irrelevant. It seems to work if the problem is the heart's architecture, or if it's in the muscle cells themselves. Even if the problem is an ion channel that's found throughout the heart, silencing this one source of noise seems to be enough to quiet the problem.

Unfortunately, these sorts of results are not unusual in biology. People who follow biomedical research superficially can be forgiven if they get the impression that there are constant promises of progress that largely remain unfulfilled. But these new findings represent real progress, even if they don't tell me, a geneticist, anything useful about a genetic disease I have. They don't help us much when it comes to treatments at the moment, and it's hard to see how they will in the immediate future.

But the knowledge won't go away, and there may well be a time where this lays the foundation for a more refined treatment than burning scar tissue into the heart.

More here:
Why understanding the genetics of my heart disease isn't much help - Ars Technica

Scientists in Brazil are taking steps towards genetically modifying sugar cane so it produces more sucrose naturally, looking to eventually boost the productivity and economic benefits of the tropical grass. Currently, it is common for producers to raise sucrose levels in sugar cane by applying artificial growth regulators or chemical ripeners. This inhibits flowering, which in turn prolongs harvest and milling periods. One of these growth regulators, ethephon, is used to manage agricultural, horticultural and forestry crops around the world. It is widely used to manipulate and stimulate the maturation of sugarcane as it contains ethylene, which is released to the plant on spraying. Ethylene, considered a ripening hormone in plants, contributes to increasing the storage of sucrose in sugar cane. "Although we knew ethylene helps increase the amount of sugar in the cane, it was not clear how the synthesis and action of this hormone affected the maturation of the plant," said Marcelo Menossi, professor at the University of Campinas (Unicamp) and coordinator of the project, which is supported by the Brazilian research foundation FAPESP. To study how ethylene acts on sugarcane, the researchers sprayed ethephon and an ethylene inhibitor, aminoethoxyvinylglycine (AVG), on sugar cane before it began to mature.

After spraying both compounds, they quantified sucrose levels in tissue samples from the leaves and stem of the cane. They did this five days after application and again 32 days later, on harvest. Those plants treated with the ethephon ripener had 60 per cent more sucrose in the upper and middle internodes at the time of harvest, while the plants treated with the AVG inhibitor had a sucrose content that was lower by 42 per cent. The researchers were then able to identify genes that respond to the action of ethylene during ripening of the sugar cane. They also successfully identified the genes involved in regulating sucrose metabolism, as well as how the hormone acts on sucrose accumulation sites in the plant. Based on the findings, the team has proposed a molecular model of how ethylene interacts with other hormones. "Knowing which genes or ripeners make it possible for the plant to increase the accumulation of sucrose will allow us to make genetic improvements in sugarcane and develop varieties that over-express these genes, without the need to apply ethylene, for example," explained Menossi. This research could also help with spotting the most productive sugar cane, as some varieties that do not respond well to hormones, he added. "It will be possible to identify those [varieties] that best express these genes and facilitate the ripening action." Taken from anewsletterbyFAPESP, aSciDev.Netdonor, edited byour Latin America and the Caribbean desk

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Genetics to boost sugarcane production - SciDev.Net

Examining 3D face models of nearly 1,000 female twins, researchers have found that the shapes of the end of the nose, the area above and below the lips, cheekbones and the inner corner of the eye are highly influenced by genetics.

The notion that our genes control our face is self-evident. Many of us have facial traits that clearly resample those of our parents and identical twins are often indistinguishable, said lead researcher Giovanni Montana, Professor at Kings College London.

However, quantifying precisely which parts of the face are strongly heritable has been challenging so far, Montana said.

For the study, published in the journal Scientific Reports, the research team took scans of twins faces using 3D cameras and custom built statistical software to generate thousands of points that were perfectly aligned across the faces and then measured how curved each face looked at each one of those locations.

The researchers then compared how similar these measurements were between identical twins, who have the same genes, and non-identical twins, who only share half of the genes.

By seeing which parts of the face are the most similar in shape in a pair of identical twins, the researchers then calculated the likelihood that the shape of that part of the face is determined by genetics.

This likelihood is quantified as the heritability, a number between zero and one, where a larger number implies that it is more likely that the shape of the face is controlled by genes, the researchers said.

By combining 3D models of the face with a statistical algorithm that measures local changes in shape, we have been able to create detailed face heritability maps, Montana said.

These maps will help identify specific genes shaping up the human face, which may also be involved in diseases altering the face morphology, Montana added.

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Genetics: A study shows which facial features are most likely to be ... - Hindustan Times

I recently had a DNA test to help trace my ancestry, and the result surprised me. The larger story might shed light on one of the grimmest and most forgotten horrors of European history, an era of brutal slave trading.

By way of background, my known genealogy is very straightforward indeed. It shows close to 100 percent Welsh not just Welsh, but one specific bit of south Welsh. That means mainly West Glamorgan, within a few miles of the city of Swansea, although with a couple of English guysin the 17th-18th centuries (In Wales, we call that diversity). Ican identify all my ancestors through all lines back to about 1840, and far beyond that in some lines.

Hence, I am near pure 100 percent Welsh on all sides. However, through the years, I have faced a nagging question. Welsh people are stereotypically short and dark, which I am not. (I am 62, and not so dark). Nor were my uncles and aunts, who were all pretty tall people. At least they were on my maternal side, and Ill explain in a moment why that distinction matters.

When I am in Europe, people all over the continent often have me marked as German, and address me as such. They greet a line of tourists like this: Good morning sir! Good morning sir! Then they come to me: Guten Tag, mein Herr! WhenI am in Norway, the locals assume I am Norwegian.

What on earth is happening? Something was amiss. I was amiss.

Hence my inspiration to take the DNA test, and the result is fascinating. (I used FamilyTreeDNA). In total contrast to the genealogy, the DNA gives me as 90 percent British Isles origins and eight percent Eastern Europe, plus a smattering from south-east Europe. Now, it never pays to take such percentages precisely, but this is suggestive. And I can confirm that Eastern Europe linkage from another source.

More specifically, I had my mitochondrial DNA done, which only traces descent in the female line mother to daughter to daughter, so that I cannot pass it on to my children. We measure this by the MtDNA haplogroup, of which there are a couple of dozen world-wide, and each is given a capital letter, so that for instance M is found among people in south east Asia, D in Japan, O in China, etc.There are also lots of subsets of those larger families. British Isles haplogroups are often J or T. The main MtDNA hapologroup in Wales is H.

My haplogroup, though, is none of the above, it is U, and specifically U4. It is in fact a striking (and quite rare) U4a1a, which points to Eastern Europe or the Baltic.

https://en.wikipedia.org/wiki/Haplogroup_U_(mtDNA)#Haplogroup_U4

Inthe available databases online, most people with that haplogroup tend to be Swedish, German, Danish, Polish . Now, that statement is a bit slanted, as these databases only include people who have paid quite a bit to get their DNA results done, so that would lead to a massive over-representation of wealthy northern Europeans. In no sense are these reliable scientific samples, nor do they say anything definitive about the actual distribution of U4 across Europe. Even so, U4 is not too common as a Welsh (or British) pattern. The furthest I can go back in my own female line is my great grandmother, and like all names on my chart, she was definitely south Welsh, with not a Pole or a Ukrainian in sight.

I should say by the way that I am not uncritically relying on these findings, which might be erroneous. But I have good reason to accept what I was told. In the paternal line, the results suggested individuals to whom I might be related, and I happen to know that those people and I share relatives with common surnames multiple generations back. There is no way a company could have cooked up such obscure, and uncannily accurate, findings. By extension then, I tend to trust the mitochondrial results.

My genealogy says one thing. My genetic information suggests something radically different.

Making life more difficult, in order to find the root of this genetic pattern, we would have to locate a woman, as only women carry MtDNA. We could not for instance assume an earlier woman in my ancestry who had a fling with a wandering Hungarian hussar in Napoleonic times. Nor, more seriously, can we invoke the many documented examples of skilled European workers traveling to Britain in early modern times, especially in pioneering Welsh industries like coal and iron. As far as I know, these visitors or migrants were all male.

So where does that U4 come from? I have an explanation not the right one, necessarily, but an interesting speculation.

Wouldnt it be wonderful if we could somehow place a woman from the Baltic/Slavic regions in South Wales in the pre-modern period, preferably very close to where my maternal family originated? Surely, that is a very tall order. Oddly enough, though, there is a historical window in which we can do something very much like that, and with remarkable geographical precision.

Over the past two centuries or so, my maternal family simply has not moved around much (Nor has my paternal line, but that is a different story). They have in fact remained within that small area of West Glamorgan, around Swansea and Neath, never really moving more than twenty miles or so in any direction. For the sake of argument, let us then assume they have in fact been in that small part of south Wales for centuries. Aha, but then we find an interesting connection. What we know about that area is that it is right next to one of the key regions of Scandinavian settlement in the British Isles in the Viking era, the ninth and tenth centuries.

The most important Scandinavian center in South Wales was Sweyns Inlet or Island, Sweyns-eye that is, Swansea. Its an open question whether Sweyn or Sveinn refers to a famous Norse king of that name, or just a lone adventurer. Near Swansea, Scandinavian names occur across the region of lower Gower, but not upper. The wonderful coastal landmark of the Worms Head in Gower is actually the head of the Ormr, Norse for a great Serpent (and it really looks like a sea serpent). A lot of the islands around the Welsh coast have pure Norse names like holm or -ey, as in Caldey. Flatholm is the Island of the Fleet. Such names scatter all across the coastal map to West Wales places like Tenby, another Scandinavian name.

Not only did the Norse name such places, but they and their descendants remained long enough to ensure that other people adopted and remembered the names. These areas were not just temporary camps: they were important enough to be real settlements, over decades or generations. At least along the coasts, the Vikings were there in force.

So what was the gender balance of these Scandinavian ventures? We tend to think of chiefs and raiders as all male communities, seizing local women, but there was more to the story. As settlements became more established, they might have brought wives or prospective (free) marriage partners. Over the years, archaeologists have recognized ever more examples of Scandinavian women buried in Britain. But other, more sinister, factors were also at work. As I say, we are looking at the 9th-10th centuries. At this very time, one of the worlds largest slave trading operations was centered on the Baltic Sea, particularly seeking out slaves from the Slav and Baltic peoples. The word slave comes from Slav, but Finland was another great center for slaves. There is a huge scholarly literature on all this.

Recent scholarship suggests that slavery and slave trading were a major incentive for the whole Viking enterprise, from the eighth century onwards. In a polygamous aristocratic society, lower status men found it hard to obtain wives within their own communities, driving them to seek women elsewhere, by force. Initially, they did this in Baltic lands like Estonia, but then mightily extended their reach. Following the rivers, some pushed deep into Russia, while others ventured into the Atlantic realms, but the basic goals remained the same. Reporting one major raid in 821, the Irish Annals of Ulster note that the heathens carried off a great number of women into captivity.

Gradually, isolated slave raids evolved into a transnational business operation that ranged across Europe, and took many slaves to the Islamic lands. Captives would have been kidnapped and taken to one of the great Swedish slave markets at Birka or Gotland, or Denmarks Hedeby. Scandinavians did much of the raiding, while Arab traders served as financiers and middlemen, and the distribution of these slave markets is indicated by the hoards of Arabic coins, dirhems, in trading centers like Birka.

A great many of those captives and slaves must have had U4 MtDNA. As we look at the map of lands where the U4 MtDNA pattern is most common, we also see the regions most heavily raided for their slaves precisely around this time.

Slave trading was thus a very large part of the economic life of the Viking world. Among other things, their enterprises ensured that large numbers of Irish and British slaves (thralls) ended up in early Iceland, where they have left a large genetic mark on the modern population. It would have been very natural for a Viking, maybe even the Sweyn who founded Swansea, to have had some slave girls along, whether as bed partners or as inventory for sale. In Iceland at least, some unfree women achieved the higher status of an acknowledged concubine, a frilla. Or possibly, a freeborn Norse woman brought along her unfree serving women and maids, even her nursemaid or her ladys maid. A female slave, by the way, was usually called an ambtt rather than a thrall. Over time, slaves might be freed and join the mainstream community.

Let us suppose that those unfree women had daughters, who intermarried with local Welsh men perhaps married, or else they were sexually exploited without their consent. They might have been sold, traded, or used as gifts. Whatever the exact process at work, any of these interactions would explain the importation of the U4 lineage into Wales.

Life for these slaves was as miserable as you might expect. In Norwegian law, slaves and thralls were described in the neuter gender: they were it rather than he or she, and were classified as just slightly superior to cattle. This is very much confirmed by the horrible portrayals of thralls that we repeatedly find in the large literature of the Icelandic sagas. But that observation leads to a major point about the nature of our historical evidence. Material evidence for free or aristocratic Scandinavian women is easy enough to find in the archaeological record, because they were deposited in substantial graves and accompanied by possessions such as brooches or other jewelry, or even weapons. Slave women, in contrast, owned nothing either in this world or in the grave, and their humble burials left very little for archaeologists to identify. You just did not bury rich grave goods when a slave woman an it died. We will likely never find material remains of Viking slaves in Britain. All they might have left just conceivably was their genes.

So could Baltic or Slavic girls have brought their MtDNA to South Wales? Very easily. Might my own maternal family even be descended from one of Sweyns slaves or concubines, someone from what we would now call Poland or Lithuania? I cant prove it, but it is plausible. If not Sweyn himself, there were lots of other comparable chieftains, who might have had girls recently imported from Birka or Gotland.

My suggestion, then, is that Slav-raiding and slave-trading are the main means by which U4 MtDNA found its way to the British Isles, and perhaps to other parts of Western Europe.

I am still puzzled by that eight-plus percent figure for my own East European blood, which goes far beyond a single woman a thousand years ago. And as I say, that element must have entered the bloodline well before the mid-nineteenth century. (Modern Wales has plenty of later migrants from that region, but they are not the explanation). I wonder: maybe those Vikings in Wales imported other slaves from the Baltic and eastern Europe, whose descendants merged completely into the local genetic mix. Their descendants perhaps became local Welsh families, called Jones or Evans, or Williams, or even Jenkins.

Even a handful of slaves leaving offspring could make a sizable genetic impact in such a tiny overall population. How many people did the whole of Wales have in, say, 1000 AD? Barely 100,000 in all? And perhaps 5,000 in West Glamorgan? Those were very small genetic pools.

What I can say confidently is that those Slavs or Balts did not originally migrate of their own accord.

For the regional context, see Michael North, The Baltic (Harvard 2015). On Viking society generally, see Jesse Byock, Viking Age Iceland (Penguin 2001). Kirsten A. Seaver has a chapter on Viking women slaves in her Thralls and Queens, in Gwyn Campbell, Suzanne Miers, and Joseph Calder Miller, eds., Women and Slavery (Ohio University Press, 2007), vol. 1: 147-167. See also Ruth Mazo Karras , Concubinage and Slavery in the Viking Age, Scandinavian Studies, 62 (1990) 141-162.

I have not read it yet, but Alice Rio has a forthcoming book on Slavery After Rome, on the period 500-1100 AD (Oxford University Press, 2017).

More here:
Of Slavs, Slaves, Vikings, and Genetics - Patheos (blog)