Speaker 1: So here's your babies in four day and as we
Speaker 1: can see, they're identical.
Speaker 2: Twins are as close as nature gets to human cloning.
Speaker 2: Their identical genetic makeup is one of the wonders of
Speaker 2: human reproduction. The close similarities can astound even identicals separated
Speaker 2: at birth often lead to strikingly similar lives with the
Speaker 2: same jobs, tastes, and hobbies, but identicals can also confound expectation.
Speaker 2: Advance in genetic science are revealing that identical twins are
Speaker 2: not as identical as we thought. Through state of the
Speaker 2: Art in the womb, four D ultrasound scans, scientifically accurate
Speaker 2: visual effects, and specially shot microscopy footage, we will reveal
Speaker 2: the hidden world of twin fetal development in a world
Speaker 2: where most of us are individual. Identical twins capture the imagination,
Speaker 2: but for scientists it's not their similarities that prove most fascinating,
Speaker 2: but their differences. They may not look it, but these
Speaker 2: boys are identical twins born with dramatically different birth weights.
Speaker 2: Twins like these with major physiological differences present an enormous
Speaker 2: opportunity to reveal truths about human identity, from fingerprints and
Speaker 2: intelligence to disease and even sexual orientation. Like everyone, identical
Speaker 2: twins begin life as a single cell a fertilized egg
Speaker 2: called a zygote. This cell contains twenty three pairs of chromosomes,
Speaker 2: tightly packed strings of genes, one set from the mother's
Speaker 2: egg and one from the father's sperm. Together, they make
Speaker 2: up the entire genetic blueprint for a new human life.
Speaker 2: A few hours after fertilization, the cell, with its cargo
Speaker 2: of chromosomes, embarks on a remarkable journey. It travels along
Speaker 2: the Filipian tube towards the womb. The single cell now
Speaker 2: starts to divide, first two, then four, then eight, each
Speaker 2: cell an identical replica of the other. This rapidly multiplying
Speaker 2: collection of cells is called a blaster, and it's here
Speaker 2: that nature's most remarkable reproductive anomaly can sometimes occur. Very occasionally,
Speaker 2: there is an event so mysterious that until recently it's
Speaker 2: never been witnessed. Several days after conception, the blastocyst spontaneously
Speaker 2: splits into two. Each new blastocyst is composed of cells
Speaker 2: with the same identical set of chromosomes, carrying the same
Speaker 2: arrangement of genes along their length. The two blastocysts now
Speaker 2: have the potential to develop into identical twins. Exactly how
Speaker 2: and why the blasticism splits is one of reeper ductive
Speaker 2: sciences greatest mysteries. But in two thousand and seven, during
Speaker 2: a laboratory study of twenty six embryos, embryologists witness this
Speaker 2: event for the first time. The blastocyst's outer membrane is
Speaker 2: called the zona pellucida, the lining inside is called the trophoblast.
Speaker 2: Just one cell layer thick, the trophoblast will eventually develop
Speaker 2: into the precenter. Within lies the inner cell mass embryonic
Speaker 2: stem cells that will eventually become the fetus. Over the
Speaker 2: course of four days, the embryologists noticed that a junction
Speaker 2: between a cell and the trophoblast membrane would regularly weaken,
Speaker 2: letting liquid leak out and causing the trothoblast to collapse
Speaker 2: like a balloon full of water. Then it would repair itself.
Speaker 2: But in two of the eggs, the embryologists spotted something
Speaker 2: no one had ever seen before. After the membrane collapsed,
Speaker 2: the inner cell mass divided in two, each clump sticking
Speaker 2: to a different side of the trough of blast as
Speaker 2: it reinflated. If these clumps were to develop in uterol,
Speaker 2: they would eventually grow into identical twins born from the
Speaker 2: same single fertilized egg. It's not surprising that most identicals
Speaker 2: retain a similar physical appearance as they grow up. Influence
Speaker 2: of genes reaches beyond how we look. Genes also affect
Speaker 2: personality and taste, making us flamboyant rather than shy, with
Speaker 2: the tape for coffee instead of tea, and a love
Speaker 2: of routine or desire for experimentation. Similarities between twins are
Speaker 2: often more than skin deep. Dennis and David Herrera of
Speaker 2: fifty three year old identicals from California. After high school,
Speaker 2: both became officers for the Los Angeles Police Department. Because
Speaker 2: they were raised together and went to the same school
Speaker 2: and had the same friends, it's impossible to say whether
Speaker 2: their career choice was influenced by their genes or their upbringing.
Speaker 2: To really test the extent to which our genes influence
Speaker 2: our life choices, scientists study identicals who have been separated
Speaker 2: at birth and raised in different environments. Daphne and Barbara
Speaker 2: were separated as babies and had no contact with each
Speaker 2: other for forty years. They were raised in very different families,
Speaker 2: one by a scientist, the other by a municipal gardener.
Speaker 2: But the similarities between them are striking and perhaps beyond coincidence.
Speaker 2: They both left school at fourteen. At sixteen, they both
Speaker 2: fell in love. In their early twenties, they each married
Speaker 2: their childhood sweethearts. They both suffered miscarriages at the same age,
Speaker 2: but went on to have children in their early twenties.
Speaker 2: Both have an irrational fear of blood and of falling down.
Speaker 2: When they met for the first time on a train platform,
Speaker 2: they wore almost identical clothing. The similarities are remarkable. They
Speaker 2: suggest that genes play a powerful role in shaping many
Speaker 2: aspects of our lives and personalities. But as we will see,
Speaker 2: it's the differences between identicals that could offer science the
Speaker 2: greatest opportunity, the chance to solve the age old debate
Speaker 2: of nature versus nurture. When these twins were born in
Speaker 2: two thousand and six, Jake weighed a healthy two and
Speaker 2: a half kilos. His twin Tom weighed just over half
Speaker 2: a chillo. Since they're identicals, this dramatic difference was a
Speaker 2: mystery for answers. Doctors look to the one environment the
Speaker 2: boys shared before birth. The womb. By day five, the
Speaker 2: two identical blastocysts have reached the womb. Now they face
Speaker 2: one of the most critical events in their nine month odyssey,
Speaker 2: one that could dramatically affect their fortunes in the womb
Speaker 2: and beyond. When they were born, Jake weighed two and
Speaker 2: a half kilos and his brother Tom half a chuilo,
Speaker 2: and yet they're identical, born just minutes apart. How could
Speaker 2: twins with the same genes look so different. The answer
Speaker 2: may lie not in their DNA, but in events that
Speaker 2: occurred in the environment they shared the womb, and the
Speaker 2: first most critical events is implantation. Around day six, the
Speaker 2: blastocyst must implant in the wall of the womb, securing
Speaker 2: its position for the next two hundred and fifty days growth,
Speaker 2: but timing is everything. Each twin will rely on a
Speaker 2: placenter to supply it with oxygen and nutrients, but the
Speaker 2: placenta only starts to develop after implantation, So blastocysts that
Speaker 2: split early before they implant each get their own placenter,
Speaker 2: but those that split late after implantation must share one.
Speaker 2: A shared placenter may mean one twin receives less nourishment
Speaker 2: than the other as a result, it grows much more slowly,
Speaker 2: a condition called selective intra uterine growth restriction. There are
Speaker 2: even rare instances when identical twins have their own presenters
Speaker 2: and yet developed this condition. Identicals Jake and Tom are
Speaker 2: one such case. Their different weights are the result of
Speaker 2: events that occurred long before they're born, but their effects
Speaker 2: may last a lifetime. In fact, the later the egg splits,
Speaker 2: the more critical the situation can become. This is Lakshmi,
Speaker 2: a three year old girl from northern India. Amazingly, only
Speaker 2: a few months ago, she had an additional set of
Speaker 2: arms and legs, and X rays revealed an extra pelvis.
Speaker 2: Strictly speaking, these don't belong to Lakshmi, but to her headless,
Speaker 2: inverted and undeveloped twin, called a parasitic twin. And yet
Speaker 2: the difference between a parasitic twin and a healthy twin
Speaker 2: is just a matter of days. In most cases, identical
Speaker 2: twins are created during a twelve to thirteen day window
Speaker 2: following fertilization. After this time, the basic embryo starts to
Speaker 2: organize itself into the first stages of the crude embryonic body.
Speaker 2: It may be that if the embryo splits during this organization,
Speaker 2: separation is never fully completed, and the two embryos remain fused.
Speaker 2: This rare reproductive accident occurs once in every two hundred
Speaker 2: thousand berths and usually results in conjoined twins. Identical twins
Speaker 2: joined at the head or body. Parasitic twins are in
Speaker 2: essence conjoined twins, except one twin is totally dependent on
Speaker 2: the other fully functional one. In Lakshmi's case, her headless
Speaker 2: twin relied entirely on her for survival. In November two
Speaker 2: thousand seven, Lakshmi underwent a delicate, twenty seven hour operation
Speaker 2: to remove the malformed twins, unwonted arms and legs, and
Speaker 2: to reconstruct her pelvis. Without this, she would most likely
Speaker 2: have died in her teens. The operation was a success
Speaker 2: and the doctor's hope she will walk unaided once implantation
Speaker 2: has occurred. Embryonic development is surprisingly rapid. By the end
Speaker 2: of the third week, a rudimentary body shape is already emerging.
Speaker 2: The embryo already resembles the beginnings of a body totally
Speaker 2: unprotected by skin and bone. On one edge, stem cells
Speaker 2: flow over and are assigned their fate by the organizer.
Speaker 2: One of the first organs to form is the heart,
Speaker 2: until now just a clump of muscle cells. Then, around
Speaker 2: day twenty two, a single cell in this dormant clump
Speaker 2: of muscle cells spontaneously contracts. It sets off a chain reaction,
Speaker 2: One after the other. Neighboring cells begin to contract until
Speaker 2: the entire vessel is pulsating. Two tiny hearts about the
Speaker 2: size of two pin heads beating together. Our twin embryos
Speaker 2: have approximately the same number of cells, the same DNA,
Speaker 2: and yet incredibly they may already be different, and those
Speaker 2: differences will become deeper and more profound as they develop,
Speaker 2: shedding light on some of the deepest mysteries of human identity.
Speaker 2: Is personality innate or learnt over time? Why do some
Speaker 2: of us succumb to disease while others remain immune? And
Speaker 2: from where do we get our skin color? What makes
Speaker 2: one person gay another straight? The answers are not as
Speaker 2: simple as we once thought. Remi and Kiran are fraternal twins,
Speaker 2: the result of two separate sperm fertilizing two separate eggs.
Speaker 2: The girl's parents are of mixed ancestry. This usually means
Speaker 2: the children will also look mixed race, but not always
Speaker 2: Being mixed ancestry means carrying a mixed set of genes
Speaker 2: for both lighter and darker skin. In Remi's case, a
Speaker 2: sperm with a set of genes that produce darker skinned
Speaker 2: children fertilized an egg with similar characteristics. In Kian's case,
Speaker 2: a sperm with genes that create lighter skin children fertilized
Speaker 2: a similar egg too. The result twins, but twins who
Speaker 2: look very different. Remi and Kian show us that twins
Speaker 2: can often confound expectation, but they are not the only ones.
Speaker 2: In two thousand and one, a pair of twins were
Speaker 2: born who at first appeared to be a boy and
Speaker 2: a girl. On closer inspection, it became clear that one
Speaker 2: had signs of both male and female genitalia. The twin
Speaker 2: was a hermaphrodite. Scientists believe that this happened because a
Speaker 2: single egg was fertilized by two sperm, one with a
Speaker 2: female sex chromosome and one with a male sex chromosome.
Speaker 2: The egg developed into a blastocyst with both male and
Speaker 2: female cells. The egg then divided, and each of the
Speaker 2: two new cells she had an extra chromosome. Resulting in
Speaker 2: a blastocyst composed of both male and female cells. That
Speaker 2: blastocyst then split to create twins. By chance. One had
Speaker 2: more cells with the male sex chrome and developed into
Speaker 2: a boy, while the other had similar numbers of cells
Speaker 2: with male and female sex chromosomes, resulting in a child
Speaker 2: with male and female genitalia. It was a startling discovery.
Speaker 2: Twins who are halfway between identical and fraternal, the only
Speaker 2: known case of semi identicals in the world. The simple
Speaker 2: classifications were used to are breaking down and will come
Speaker 2: to inform much of our newer understanding about how twins,
Speaker 2: and by extension, all of us develop. At five weeks,
Speaker 2: our identical twin embryos are beginning to take shape. Now
Speaker 2: curved into a C shape, their heads and tails can
Speaker 2: be distincts, as can hearts, spinal columns, and the beginnings
Speaker 2: of tiny limbuds. At this stage, the embryo looks almost
Speaker 2: indistinguishable to any vertebrate in the animal kingdom. These fragile creatures,
Speaker 2: just one and a half millimeters long, are about to
Speaker 2: embark on a critical period of brain development. This five
Speaker 2: week milestone could be another stage where identicals develop key
Speaker 2: differences before they're even born. Salsau and Jesus are identical twins.
Speaker 2: They were raised together. As they grew up, they remained
Speaker 2: physically similar, but their tastes and interests began to diverge.
Speaker 2: Celso became interested in dance and academia, while Jazeus preferred sports.
Speaker 2: The most surprising difference between the two brothers is that
Speaker 2: Celso here wearing black, is gay. The differing sexual orientation
Speaker 2: of identical twins is an opportunity to investigate one of
Speaker 2: science's most controversial questions. Are people born gay? As Celsou
Speaker 2: and Jazeus were raised by the same parents in the
Speaker 2: same household, they inevitably shared the same environment at a
Speaker 2: crucial time in their personal development. In the general population,
Speaker 2: the chance of someone being gay is less than five
Speaker 2: percent unless you have a gay twin. Here, the chances
Speaker 2: are much higher. If you're fraternal, sharing half your genes,
Speaker 2: there's nearly a twenty five percent chance that you will
Speaker 2: also be gay. If you're identical, sharing all your genes,
Speaker 2: there's roughly a fifty percent chance that you will also
Speaker 2: be gay. This suggests that there must be some genetic
Speaker 2: component to our sexuality. However, it can't be all down
Speaker 2: to genes. Otherwise all identicals would be either both gay
Speaker 2: or both straight. Some other factor must be at play.
Speaker 2: In their first few weeks, all fetuses develop along similar lines.
Speaker 2: If nothing changed, we would all be born. Female. Fetuses
Speaker 2: with the male Y chromosome will form testes at about
Speaker 2: week six that begin to produce the hormone testosterone, but
Speaker 2: at about the eighth week, testosterone is released and may
Speaker 2: affect early brain development. This hormone masculinizes the body. Testosterone
Speaker 2: also masculinizes the brain, including a part called the hypothalamus,
Speaker 2: part of the network which controls who we find sexually attractive.
Speaker 2: Some scientists believe that the more the hypothalamus is exposed
Speaker 2: to testosterone, the more it sets the stage for a
Speaker 2: sexual inclination towards women. Occasionally, a male fetus may not
Speaker 2: produce sufficient testosterone or its brain does not absorb enough
Speaker 2: to shape it along heterosexual nines. If this theory is right,
Speaker 2: then it may be that Celso the gay brother, absorbed
Speaker 2: enough testosterone to masculinize his body, but not enough to
Speaker 2: fully differentiate his brain. As a result, he was left
Speaker 2: with a desire for men. Although there are still many
Speaker 2: mysteries twins like these are playing a crucial role in
Speaker 2: informing scientists about how and when we all develop our sexuality.
Speaker 2: By the eighth week, our identical twins have finished their
Speaker 2: embryonic stage of development and are now known as fetuses
Speaker 2: from the Latin meaning offspring. The twins, now secure in
Speaker 2: their own sex but sharing a percenter, have approximately two
Speaker 2: hundred days left until birth. Now their growth accelerates. By
Speaker 2: thirteen weeks, they're beginning to look more human. The eyes
Speaker 2: have moved together and the head is in better proportion
Speaker 2: to the rest of the body. It's also the end
Speaker 2: of the first trimester, the time most pregnant women will
Speaker 2: have their initial ultrasound scan. The ultrasound sonographer checks for
Speaker 2: basic signs of normal development.
Speaker 1: So here's your babies in four D. And as we
Speaker 1: can see the identical.
Speaker 2: The sonographer sees a single placenta, a sure sign that
Speaker 2: the twins are identical.
Speaker 1: We can see here a single percenter like a T section,
Speaker 1: in which proves that you're having identical twins. So when
Speaker 1: would you see them start interacting or reacting against each other.
Speaker 1: We can see them almost sort of moving.
Speaker 2: From now on, the mother will be monitored closely twin
Speaker 2: pregnancies are more at risk of premature births. Immature development
Speaker 2: of lungs and organs can lead to complications. These complications
Speaker 2: make natural childbirth more dangerous. As a result, twins are
Speaker 2: around fifty percent more likely to be borne by cesarean
Speaker 2: section than Singleton's. The timing of the scan also marks
Speaker 2: the start of the second trimester. The second trimester, from
Speaker 2: twelve to twenty four weeks, will see not only dramatic growth,
Speaker 2: but massive development in everything from the structure of the
Speaker 2: brain to the refinement of facial features. By the end
Speaker 2: of this stage, the fetuses will be small but almost
Speaker 2: perfectly formed. They look very similar, but newer search reveals
Speaker 2: that even at this early stage, identical twins may already
Speaker 2: be less identical. Subtle changes are under way that will
Speaker 2: become greater throughout their lives, and the mechanism responsible is
Speaker 2: one of the most complex yet fascinating processes in the
Speaker 2: whole of human development. Fifteen weeks into their journey from
Speaker 2: conception to birth, our identical twins begin to move for
Speaker 2: the first time. They start to interact, exploring their environment
Speaker 2: with their hands and feet, touching and even appearing to
Speaker 2: kiss their mother. In later pregnancy will feel the same case.
Speaker 2: Each twin feels in muteroe. At times they appear aggressive,
Speaker 2: at others almost caring. They look identical, but unseen influences
Speaker 2: may already be taking effect, ones that could subtly alter
Speaker 2: the expression of genes in their growing body identicals. Jake
Speaker 2: and Tom are now aged seventeen months. Jake is eight
Speaker 2: centimeters taller than Tom and four kilos heavier When they
Speaker 2: were born in two thousand and six, doctors attributed these
Speaker 2: discrepancies in size and weight to restricted nutrition or blood
Speaker 2: flow in the womb. They expected Tom to catch up,
Speaker 2: but after a year and a half, they're investigating whether
Speaker 2: Tom may be suffering from a genetic condition called Russell's
Speaker 2: Silver syndrome, a growth disorder. One of the causes of
Speaker 2: this syndrome may be a problem with a growth gene
Speaker 2: on chromosome eleven. Scientists are puzzling over why Tom and
Speaker 2: his brother do not both have a syndrome. Identical twins,
Speaker 2: after all, have identical genes. Genetic puzzles like these are
Speaker 2: opening up a little known world at the outer reaches
Speaker 2: of science, epigenetics. This growing field of biology may help
Speaker 2: explain the differences between twins like Tom and Jake. Epigenetic
Speaker 2: reveals that while their DNA code may be the same,
Speaker 2: the way it functions can differ. The human genome contains
Speaker 2: around twenty five thousand genes, each with its own specific function,
Speaker 2: such as producing energy or directing cell division. Now geneticists
Speaker 2: are investigating a previously unknown aspect of the genome called
Speaker 2: the epigenome. There is a series of chemicals that act
Speaker 2: as switches capable of activating or deactivating individual genes. One
Speaker 2: of these switches works by a process called DNA methylation.
Speaker 2: This causes enzymes insider cell to attach a minuscule molecular
Speaker 2: compound a methyl group, to a gene. This compound can
Speaker 2: deactivate or at times activate the gene, but the gene
Speaker 2: remains the cell's DNA profile is unchaeed changed. This could
Speaker 2: explain the difference between identical twins Jake and Tom. Some
Speaker 2: as yet unidentified environmental factor in early cell development has
Speaker 2: caused a methyl group to attach itself to a gene
Speaker 2: on one of Tom's chromosomes, a gene associated with growth.
Speaker 2: The growth gene is still there, but it's been switched off.
Speaker 2: By investigating the mystery of twins like Tom and Jake,
Speaker 2: Geneticists are finally beginning to find clues to some of
Speaker 2: the great mysteries of the human genome. This is a
Speaker 2: map of chromosomes belonging to identical twins from age three
Speaker 2: on the left to twins aged fifteen on the right.
Speaker 2: The red markings are an indication of the increase in
Speaker 2: the methylation that has occurred to their chromosomes over half
Speaker 2: a century. We know that factors like smoking, diet, and
Speaker 2: chemical exposure can, over a lifetime, wreak havoc with how
Speaker 2: genes operate. What's astounding is that there are different environmental
Speaker 2: influences in not only our lifetime, but also in utero. Hormones, space,
Speaker 2: quality of nutrition can all affect identical embryos differently, even
Speaker 2: those sharing a placenta. The activation and deactivation of genes
Speaker 2: during early development could explain many of the twists of
Speaker 2: fate that affect us all why one person is struck
Speaker 2: by disease while another spared. Epigenetics may also play a
Speaker 2: significant role in determining sexuality. If sexual preference is associated
Speaker 2: with an asthet unidentified gene, it may be that the
Speaker 2: epigenetic suppression or activation of this gene dictates sexual preference.
Speaker 2: These genetic switches may be the answer to why one
Speaker 2: twin absorbs more testosterone than the other, resulting in one
Speaker 2: being gay and the other straight. It's becoming clear that
Speaker 2: our health, personality, tastes, and even appearance are not the
Speaker 2: product of either our genes or our environment, but that
Speaker 2: nature and nurture are inextricably bound, with epigenetics the tangible
Speaker 2: biological link between the two, and most surprisingly of all,
Speaker 2: new research claims these subtle changes to a gene's expression
Speaker 2: can be passed on down through the generations without affecting
Speaker 2: the underlying DNA. Studying a register of births and deaths
Speaker 2: in a remote region of northern Sweden, researchers noticed a
Speaker 2: peculiar phenomenon. A generation of boys who experienced a famine
Speaker 2: had grandchildren who led longer lives. On the other hand,
Speaker 2: descendants of those boys who enjoyed plentiful food as children
Speaker 2: experienced an increased risk of diabetes, cardiovascular disease, and higher
Speaker 2: mortality rates. The effect of famine was especially strong if
Speaker 2: the boy was at the age when he was just
Speaker 2: about to start producing reproductive cells his sperm. It seems
Speaker 2: the genetic makeup of these reproductive cells were directly but
Speaker 2: subtly altered by the famine or feast. Through their sperm,
Speaker 2: they passed on a nutritional legacy to future generations. The
Speaker 2: more we explore the hidden world of epigenetics, the more
Speaker 2: it seems we are not simply a product of our genes.
Speaker 2: We may even have the power to steer our genetic
Speaker 2: destiny and perhaps that of our descendants, through lifestyle choices
Speaker 2: such as smoking, diet, and exercise. What makes identicals unique
Speaker 2: and useful to genetics is that their genome is one
Speaker 2: hundred percent match, or at least that's what we thought. Now,
Speaker 2: powerful new DNA techniques are revealing a different story, one
Speaker 2: that is only just unfolding. As the second trimester draws
Speaker 2: to a close, the twins will have a second scan.
Speaker 2: The development of external features such as limbs and eyes
Speaker 2: will be checked, and the major organs will be examined
Speaker 2: for signs of defects. The twins are about twenty centimeters long,
Speaker 2: small enough to cradle in the palm of the hand.
Speaker 2: The twenty week scan is the time when most mothers
Speaker 2: will discover whether they're having a boy or a girl.
Speaker 2: Gender identification can be done as early as eleven to
Speaker 2: twelve weeks, but is more certain at the four months scan.
Speaker 2: The scan reveals our twins are boys. Our twins are
Speaker 2: twenty four weeks into development. Their mother can now feel
Speaker 2: them kick inside the wound. A battle for space is raging.
Speaker 2: A scan reveals this struggle and perhaps even a glimpse
Speaker 2: of emerging personalities. Ultrasound studies combined with observations of twins
Speaker 2: after birth, show very early forms of shy or extrovert behavior.
Speaker 2: In one study of fraternal twins, the shire twin would
Speaker 2: occasionally hang onto his umbilical cord and even appear to
Speaker 2: lick it, while his sister would seek to grab, kick,
Speaker 2: and push him. Intriguingly, this pattern continued after birth. At
Speaker 2: four years of age, the shy twin still exhibited retiring behavior,
Speaker 2: while his more extrovert sister would try to grab and
Speaker 2: play with him. It seems our personalities may well begin
Speaker 2: to form in the womb. From week twenty nine onwards,
Speaker 2: the fetuses are beginning to resemble newborn babies. Their body
Speaker 2: fat rapidly increases, bones are fully developed but still soft
Speaker 2: and pliable. Head hair grows thicker, and fingernails reach the fingertips. Already,
Speaker 2: our twins' fingerprints are different. Epigenetic changes have already impacted
Speaker 2: the genes that control the pattern of the fingertips. These
Speaker 2: fingerprint differences will become more pronounced as the fingertips develop.
Speaker 2: They receive blood from the veins. This makes them swell,
Speaker 2: forming distinctive fingerprint patterns. If blood flow from the percenter
Speaker 2: in one twin is restricted, blood may be directed away
Speaker 2: from the fingers and other extremities, leaving this twin with
Speaker 2: more wells on their fingerprints than the other. Our fingerprint
Speaker 2: patterns can help to indicate how unhealthy our heart will
Speaker 2: be in adult life. The more wells, the greater the
Speaker 2: chance of later heart problems. From the moment a fertilized
Speaker 2: egg divides in two, various influences on the genetic code
Speaker 2: conspire to create differences between identical twins, differences that can
Speaker 2: become more pronounced over time. Yet it's always been assumed
Speaker 2: that identical twins share identical DNA until a discovery in
Speaker 2: two thousand and seven surprised the scientific world. Researchers set
Speaker 2: out to investigate one of the most puzzling anomalies in
Speaker 2: the life of twins, why one succumbs to a genetically
Speaker 2: inherited disease while the other is unaffected. They chose Parkinson's
Speaker 2: because it's more likely to be caused by a spontaneous
Speaker 2: genetic cause than be inherited. So the scientists examined the
Speaker 2: genes of nineteen pairs of identical twins, including nine pairs
Speaker 2: in which only one twin showed signs of the genetic disorder.
Speaker 2: They wanted to challenge the common perception that identicals are
Speaker 2: genetically identical. Indeed, their analysis showed that there were differences
Speaker 2: between the number of genes each twin had. Genes usually
Speaker 2: occur in two copies, one inherited from each parent, but
Speaker 2: this study has revealed it's possible to have just one copy,
Speaker 2: or to have three or more copies of the same gene.
Speaker 2: This phenomenon, called copy number variation, can fundamentally alter the
Speaker 2: genes function and may induce the disease in one twin
Speaker 2: and not the other. It's a major breakthrough in our
Speaker 2: understanding of disease and in the study of twins, because
Speaker 2: the discovery means that identicals are not a one hundred
Speaker 2: percent genetic match. The very definition of identical twins needs
Speaker 2: to be revised, as advances in technology can prove that
Speaker 2: small but significant changes are present in all identical twins.
Speaker 2: Our identical twin boys are approaching full urn already. There
Speaker 2: will be subtle genetic differences between them that may shape
Speaker 2: very different futures. But first they must face the most
Speaker 2: dangerous stage of their long journey in the womb, the birth.
Speaker 2: It's thirty five weeks. The twins are now fully developed.
Speaker 2: They have hair, eyelashes, nails, and can open and close
Speaker 2: their eyes and mouths. Conditions in the womb are becoming cramped,
Speaker 2: but around two kilos each weighs about a third less
Speaker 2: than the average singleton baby, but combined they put tremendous
Speaker 2: pressure on the womb. Premature deliveries for twins before full
Speaker 2: term at thirty seven weeks are common. Our twins will
Speaker 2: be borne at week thirty five by cesarean section. About
Speaker 2: half of twins are delivered this way due to the
Speaker 2: difficulties and dangers of giving birth to two babies naturally.
Speaker 2: To ensure safety, there is a larger than normal delivery
Speaker 2: team on hand. The obstetrician swiftly cuts the first membrane
Speaker 2: and then the second Caesareans are always performed quickly to
Speaker 2: reduce the risks of complications. He plunges his hand into
Speaker 2: the womb and takes the first baby out. The baby
Speaker 2: takes his first breath and emits a healthy screen. The
Speaker 2: cord to the placenta, his lifeline for the last thirty
Speaker 2: five weeks is finally cut. Working briskly, the surgeon looks
Speaker 2: for his twin. With his twin brother out of the way,
Speaker 2: he follows quickly, also paid first. Following birth. It's not
Speaker 2: always obvious to the obstetrician whether the twins are identical
Speaker 2: or fraternal. Our twins have a shared placenter, the clearest
Speaker 2: indication that they are identical. If the identicals have separate percenters,
Speaker 2: as happens occasionally, DNA analysis is the only sure method
Speaker 2: of identification. After an extraordinary journey, our two reproductive marvels
Speaker 2: have made it safely into the world. They may look alike,
Speaker 2: but we now know they are already different. Two hundred
Speaker 2: and forty five days ago, a fertilized egg divided, creating
Speaker 2: two identical embryos. From that moment onwards, their paths began
Speaker 2: to diverge. Inequalities in nutrition or space, differing exposure to hormones,
Speaker 2: small alterations in their epigenetic profiling, even minute differences in
Speaker 2: the underlying genome, all combined to create subtle, yet significant differences.
Speaker 2: Now the twins are about to embark on the next
Speaker 2: stage of their journey. As they grow, facing diverse experiences
Speaker 2: and influences, the differences between them will become ever greater.
Speaker 2: These differences bring us closer to answering some of humanity's
Speaker 2: most profound questions. The study of identical twins has shed
Speaker 2: new light on the complex mix of genetics and environment,
Speaker 2: nature and nurture that makes each of us unique. It
Speaker 2: has profound and far reaching implications for how we all
Speaker 2: lead our lives.