WEBVTT

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<v Speaker 1>So here's your babies in four day and as we

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<v Speaker 1>can see, they're identical.

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<v Speaker 2>Twins are as close as nature gets to human cloning.

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<v Speaker 2>Their identical genetic makeup is one of the wonders of

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<v Speaker 2>human reproduction. The close similarities can astound even identicals separated

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<v Speaker 2>at birth often lead to strikingly similar lives with the

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<v Speaker 2>same jobs, tastes, and hobbies, but identicals can also confound expectation.

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<v Speaker 2>Advance in genetic science are revealing that identical twins are

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<v Speaker 2>not as identical as we thought. Through state of the

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<v Speaker 2>Art in the womb, four D ultrasound scans, scientifically accurate

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<v Speaker 2>visual effects, and specially shot microscopy footage, we will reveal

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<v Speaker 2>the hidden world of twin fetal development in a world

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<v Speaker 2>where most of us are individual. Identical twins capture the imagination,

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<v Speaker 2>but for scientists it's not their similarities that prove most fascinating,

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<v Speaker 2>but their differences. They may not look it, but these

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<v Speaker 2>boys are identical twins born with dramatically different birth weights.

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<v Speaker 2>Twins like these with major physiological differences present an enormous

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<v Speaker 2>opportunity to reveal truths about human identity, from fingerprints and

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<v Speaker 2>intelligence to disease and even sexual orientation. Like everyone, identical

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<v Speaker 2>twins begin life as a single cell a fertilized egg

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<v Speaker 2>called a zygote. This cell contains twenty three pairs of chromosomes,

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<v Speaker 2>tightly packed strings of genes, one set from the mother's

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<v Speaker 2>egg and one from the father's sperm. Together, they make

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<v Speaker 2>up the entire genetic blueprint for a new human life.

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<v Speaker 2>A few hours after fertilization, the cell, with its cargo

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<v Speaker 2>of chromosomes, embarks on a remarkable journey. It travels along

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<v Speaker 2>the Filipian tube towards the womb. The single cell now

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<v Speaker 2>starts to divide, first two, then four, then eight, each

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<v Speaker 2>cell an identical replica of the other. This rapidly multiplying

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<v Speaker 2>collection of cells is called a blaster, and it's here

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<v Speaker 2>that nature's most remarkable reproductive anomaly can sometimes occur. Very occasionally,

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<v Speaker 2>there is an event so mysterious that until recently it's

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<v Speaker 2>never been witnessed. Several days after conception, the blastocyst spontaneously

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<v Speaker 2>splits into two. Each new blastocyst is composed of cells

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<v Speaker 2>with the same identical set of chromosomes, carrying the same

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<v Speaker 2>arrangement of genes along their length. The two blastocysts now

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<v Speaker 2>have the potential to develop into identical twins. Exactly how

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<v Speaker 2>and why the blasticism splits is one of reeper ductive

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<v Speaker 2>sciences greatest mysteries. But in two thousand and seven, during

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<v Speaker 2>a laboratory study of twenty six embryos, embryologists witness this

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<v Speaker 2>event for the first time. The blastocyst's outer membrane is

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<v Speaker 2>called the zona pellucida, the lining inside is called the trophoblast.

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<v Speaker 2>Just one cell layer thick, the trophoblast will eventually develop

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<v Speaker 2>into the precenter. Within lies the inner cell mass embryonic

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<v Speaker 2>stem cells that will eventually become the fetus. Over the

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<v Speaker 2>course of four days, the embryologists noticed that a junction

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<v Speaker 2>between a cell and the trophoblast membrane would regularly weaken,

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<v Speaker 2>letting liquid leak out and causing the trothoblast to collapse

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<v Speaker 2>like a balloon full of water. Then it would repair itself.

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<v Speaker 2>But in two of the eggs, the embryologists spotted something

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<v Speaker 2>no one had ever seen before. After the membrane collapsed,

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<v Speaker 2>the inner cell mass divided in two, each clump sticking

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<v Speaker 2>to a different side of the trough of blast as

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<v Speaker 2>it reinflated. If these clumps were to develop in uterol,

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<v Speaker 2>they would eventually grow into identical twins born from the

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<v Speaker 2>same single fertilized egg. It's not surprising that most identicals

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<v Speaker 2>retain a similar physical appearance as they grow up. Influence

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<v Speaker 2>of genes reaches beyond how we look. Genes also affect

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<v Speaker 2>personality and taste, making us flamboyant rather than shy, with

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<v Speaker 2>the tape for coffee instead of tea, and a love

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<v Speaker 2>of routine or desire for experimentation. Similarities between twins are

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<v Speaker 2>often more than skin deep. Dennis and David Herrera of

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<v Speaker 2>fifty three year old identicals from California. After high school,

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<v Speaker 2>both became officers for the Los Angeles Police Department. Because

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<v Speaker 2>they were raised together and went to the same school

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<v Speaker 2>and had the same friends, it's impossible to say whether

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<v Speaker 2>their career choice was influenced by their genes or their upbringing.

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<v Speaker 2>To really test the extent to which our genes influence

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<v Speaker 2>our life choices, scientists study identicals who have been separated

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<v Speaker 2>at birth and raised in different environments. Daphne and Barbara

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<v Speaker 2>were separated as babies and had no contact with each

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<v Speaker 2>other for forty years. They were raised in very different families,

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<v Speaker 2>one by a scientist, the other by a municipal gardener.

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<v Speaker 2>But the similarities between them are striking and perhaps beyond coincidence.

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<v Speaker 2>They both left school at fourteen. At sixteen, they both

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<v Speaker 2>fell in love. In their early twenties, they each married

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<v Speaker 2>their childhood sweethearts. They both suffered miscarriages at the same age,

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<v Speaker 2>but went on to have children in their early twenties.

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<v Speaker 2>Both have an irrational fear of blood and of falling down.

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<v Speaker 2>When they met for the first time on a train platform,

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<v Speaker 2>they wore almost identical clothing. The similarities are remarkable. They

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<v Speaker 2>suggest that genes play a powerful role in shaping many

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<v Speaker 2>aspects of our lives and personalities. But as we will see,

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<v Speaker 2>it's the differences between identicals that could offer science the

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<v Speaker 2>greatest opportunity, the chance to solve the age old debate

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<v Speaker 2>of nature versus nurture. When these twins were born in

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<v Speaker 2>two thousand and six, Jake weighed a healthy two and

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<v Speaker 2>a half kilos. His twin Tom weighed just over half

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<v Speaker 2>a chillo. Since they're identicals, this dramatic difference was a

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<v Speaker 2>mystery for answers. Doctors look to the one environment the

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<v Speaker 2>boys shared before birth. The womb. By day five, the

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<v Speaker 2>two identical blastocysts have reached the womb. Now they face

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<v Speaker 2>one of the most critical events in their nine month odyssey,

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<v Speaker 2>one that could dramatically affect their fortunes in the womb

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<v Speaker 2>and beyond. When they were born, Jake weighed two and

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<v Speaker 2>a half kilos and his brother Tom half a chuilo,

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<v Speaker 2>and yet they're identical, born just minutes apart. How could

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<v Speaker 2>twins with the same genes look so different. The answer

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<v Speaker 2>may lie not in their DNA, but in events that

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<v Speaker 2>occurred in the environment they shared the womb, and the

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<v Speaker 2>first most critical events is implantation. Around day six, the

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<v Speaker 2>blastocyst must implant in the wall of the womb, securing

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<v Speaker 2>its position for the next two hundred and fifty days growth,

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<v Speaker 2>but timing is everything. Each twin will rely on a

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<v Speaker 2>placenter to supply it with oxygen and nutrients, but the

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<v Speaker 2>placenta only starts to develop after implantation, So blastocysts that

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<v Speaker 2>split early before they implant each get their own placenter,

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<v Speaker 2>but those that split late after implantation must share one.

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<v Speaker 2>A shared placenter may mean one twin receives less nourishment

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<v Speaker 2>than the other as a result, it grows much more slowly,

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<v Speaker 2>a condition called selective intra uterine growth restriction. There are

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<v Speaker 2>even rare instances when identical twins have their own presenters

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<v Speaker 2>and yet developed this condition. Identicals Jake and Tom are

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<v Speaker 2>one such case. Their different weights are the result of

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<v Speaker 2>events that occurred long before they're born, but their effects

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<v Speaker 2>may last a lifetime. In fact, the later the egg splits,

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<v Speaker 2>the more critical the situation can become. This is Lakshmi,

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<v Speaker 2>a three year old girl from northern India. Amazingly, only

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<v Speaker 2>a few months ago, she had an additional set of

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<v Speaker 2>arms and legs, and X rays revealed an extra pelvis.

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<v Speaker 2>Strictly speaking, these don't belong to Lakshmi, but to her headless,

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<v Speaker 2>inverted and undeveloped twin, called a parasitic twin. And yet

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<v Speaker 2>the difference between a parasitic twin and a healthy twin

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<v Speaker 2>is just a matter of days. In most cases, identical

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<v Speaker 2>twins are created during a twelve to thirteen day window

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<v Speaker 2>following fertilization. After this time, the basic embryo starts to

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<v Speaker 2>organize itself into the first stages of the crude embryonic body.

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<v Speaker 2>It may be that if the embryo splits during this organization,

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<v Speaker 2>separation is never fully completed, and the two embryos remain fused.

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<v Speaker 2>This rare reproductive accident occurs once in every two hundred

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<v Speaker 2>thousand berths and usually results in conjoined twins. Identical twins

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<v Speaker 2>joined at the head or body. Parasitic twins are in

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<v Speaker 2>essence conjoined twins, except one twin is totally dependent on

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<v Speaker 2>the other fully functional one. In Lakshmi's case, her headless

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<v Speaker 2>twin relied entirely on her for survival. In November two

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<v Speaker 2>thousand seven, Lakshmi underwent a delicate, twenty seven hour operation

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<v Speaker 2>to remove the malformed twins, unwonted arms and legs, and

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<v Speaker 2>to reconstruct her pelvis. Without this, she would most likely

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<v Speaker 2>have died in her teens. The operation was a success

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<v Speaker 2>and the doctor's hope she will walk unaided once implantation

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<v Speaker 2>has occurred. Embryonic development is surprisingly rapid. By the end

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<v Speaker 2>of the third week, a rudimentary body shape is already emerging.

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<v Speaker 2>The embryo already resembles the beginnings of a body totally

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<v Speaker 2>unprotected by skin and bone. On one edge, stem cells

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<v Speaker 2>flow over and are assigned their fate by the organizer.

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<v Speaker 2>One of the first organs to form is the heart,

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<v Speaker 2>until now just a clump of muscle cells. Then, around

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<v Speaker 2>day twenty two, a single cell in this dormant clump

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<v Speaker 2>of muscle cells spontaneously contracts. It sets off a chain reaction,

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<v Speaker 2>One after the other. Neighboring cells begin to contract until

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<v Speaker 2>the entire vessel is pulsating. Two tiny hearts about the

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<v Speaker 2>size of two pin heads beating together. Our twin embryos

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<v Speaker 2>have approximately the same number of cells, the same DNA,

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<v Speaker 2>and yet incredibly they may already be different, and those

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<v Speaker 2>differences will become deeper and more profound as they develop,

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<v Speaker 2>shedding light on some of the deepest mysteries of human identity.

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<v Speaker 2>Is personality innate or learnt over time? Why do some

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<v Speaker 2>of us succumb to disease while others remain immune? And

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<v Speaker 2>from where do we get our skin color? What makes

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<v Speaker 2>one person gay another straight? The answers are not as

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<v Speaker 2>simple as we once thought. Remi and Kiran are fraternal twins,

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<v Speaker 2>the result of two separate sperm fertilizing two separate eggs.

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<v Speaker 2>The girl's parents are of mixed ancestry. This usually means

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<v Speaker 2>the children will also look mixed race, but not always

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<v Speaker 2>Being mixed ancestry means carrying a mixed set of genes

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<v Speaker 2>for both lighter and darker skin. In Remi's case, a

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<v Speaker 2>sperm with a set of genes that produce darker skinned

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<v Speaker 2>children fertilized an egg with similar characteristics. In Kian's case,

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<v Speaker 2>a sperm with genes that create lighter skin children fertilized

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<v Speaker 2>a similar egg too. The result twins, but twins who

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<v Speaker 2>look very different. Remi and Kian show us that twins

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<v Speaker 2>can often confound expectation, but they are not the only ones.

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<v Speaker 2>In two thousand and one, a pair of twins were

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<v Speaker 2>born who at first appeared to be a boy and

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<v Speaker 2>a girl. On closer inspection, it became clear that one

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<v Speaker 2>had signs of both male and female genitalia. The twin

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<v Speaker 2>was a hermaphrodite. Scientists believe that this happened because a

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<v Speaker 2>single egg was fertilized by two sperm, one with a

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<v Speaker 2>female sex chromosome and one with a male sex chromosome.

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<v Speaker 2>The egg developed into a blastocyst with both male and

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<v Speaker 2>female cells. The egg then divided, and each of the

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<v Speaker 2>two new cells she had an extra chromosome. Resulting in

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<v Speaker 2>a blastocyst composed of both male and female cells. That

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<v Speaker 2>blastocyst then split to create twins. By chance. One had

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<v Speaker 2>more cells with the male sex chrome and developed into

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<v Speaker 2>a boy, while the other had similar numbers of cells

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<v Speaker 2>with male and female sex chromosomes, resulting in a child

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<v Speaker 2>with male and female genitalia. It was a startling discovery.

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<v Speaker 2>Twins who are halfway between identical and fraternal, the only

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<v Speaker 2>known case of semi identicals in the world. The simple

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<v Speaker 2>classifications were used to are breaking down and will come

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<v Speaker 2>to inform much of our newer understanding about how twins,

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<v Speaker 2>and by extension, all of us develop. At five weeks,

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<v Speaker 2>our identical twin embryos are beginning to take shape. Now

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<v Speaker 2>curved into a C shape, their heads and tails can

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<v Speaker 2>be distincts, as can hearts, spinal columns, and the beginnings

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<v Speaker 2>of tiny limbuds. At this stage, the embryo looks almost

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<v Speaker 2>indistinguishable to any vertebrate in the animal kingdom. These fragile creatures,

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<v Speaker 2>just one and a half millimeters long, are about to

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<v Speaker 2>embark on a critical period of brain development. This five

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<v Speaker 2>week milestone could be another stage where identicals develop key

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<v Speaker 2>differences before they're even born. Salsau and Jesus are identical twins.

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<v Speaker 2>They were raised together. As they grew up, they remained

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<v Speaker 2>physically similar, but their tastes and interests began to diverge.

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<v Speaker 2>Celso became interested in dance and academia, while Jazeus preferred sports.

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<v Speaker 2>The most surprising difference between the two brothers is that

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<v Speaker 2>Celso here wearing black, is gay. The differing sexual orientation

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<v Speaker 2>of identical twins is an opportunity to investigate one of

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<v Speaker 2>science's most controversial questions. Are people born gay? As Celsou

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<v Speaker 2>and Jazeus were raised by the same parents in the

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<v Speaker 2>same household, they inevitably shared the same environment at a

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<v Speaker 2>crucial time in their personal development. In the general population,

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<v Speaker 2>the chance of someone being gay is less than five

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<v Speaker 2>percent unless you have a gay twin. Here, the chances

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<v Speaker 2>are much higher. If you're fraternal, sharing half your genes,

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<v Speaker 2>there's nearly a twenty five percent chance that you will

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<v Speaker 2>also be gay. If you're identical, sharing all your genes,

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<v Speaker 2>there's roughly a fifty percent chance that you will also

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<v Speaker 2>be gay. This suggests that there must be some genetic

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00:23:38.000 --> 00:23:48.319
<v Speaker 2>component to our sexuality. However, it can't be all down

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<v Speaker 2>to genes. Otherwise all identicals would be either both gay

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<v Speaker 2>or both straight. Some other factor must be at play.

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<v Speaker 2>In their first few weeks, all fetuses develop along similar lines.

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<v Speaker 2>If nothing changed, we would all be born. Female. Fetuses

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<v Speaker 2>with the male Y chromosome will form testes at about

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<v Speaker 2>week six that begin to produce the hormone testosterone, but

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<v Speaker 2>at about the eighth week, testosterone is released and may

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<v Speaker 2>affect early brain development. This hormone masculinizes the body. Testosterone

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<v Speaker 2>also masculinizes the brain, including a part called the hypothalamus,

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<v Speaker 2>part of the network which controls who we find sexually attractive.

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<v Speaker 2>Some scientists believe that the more the hypothalamus is exposed

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<v Speaker 2>to testosterone, the more it sets the stage for a

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00:24:58.359 --> 00:25:09.440
<v Speaker 2>sexual inclination towards women. Occasionally, a male fetus may not

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<v Speaker 2>produce sufficient testosterone or its brain does not absorb enough

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00:25:13.759 --> 00:25:19.119
<v Speaker 2>to shape it along heterosexual nines. If this theory is right,

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<v Speaker 2>then it may be that Celso the gay brother, absorbed

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00:25:23.039 --> 00:25:27.079
<v Speaker 2>enough testosterone to masculinize his body, but not enough to

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00:25:27.119 --> 00:25:31.599
<v Speaker 2>fully differentiate his brain. As a result, he was left

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00:25:31.599 --> 00:25:42.000
<v Speaker 2>with a desire for men. Although there are still many

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<v Speaker 2>mysteries twins like these are playing a crucial role in

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<v Speaker 2>informing scientists about how and when we all develop our sexuality.

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<v Speaker 2>By the eighth week, our identical twins have finished their

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<v Speaker 2>embryonic stage of development and are now known as fetuses

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00:26:03.400 --> 00:26:11.119
<v Speaker 2>from the Latin meaning offspring. The twins, now secure in

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00:26:11.160 --> 00:26:15.519
<v Speaker 2>their own sex but sharing a percenter, have approximately two

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00:26:15.640 --> 00:26:26.640
<v Speaker 2>hundred days left until birth. Now their growth accelerates. By

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00:26:26.680 --> 00:26:35.000
<v Speaker 2>thirteen weeks, they're beginning to look more human. The eyes

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00:26:35.000 --> 00:26:39.279
<v Speaker 2>have moved together and the head is in better proportion

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00:26:39.359 --> 00:26:48.000
<v Speaker 2>to the rest of the body. It's also the end

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00:26:48.079 --> 00:26:52.079
<v Speaker 2>of the first trimester, the time most pregnant women will

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00:26:52.079 --> 00:27:02.519
<v Speaker 2>have their initial ultrasound scan. The ultrasound sonographer checks for

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<v Speaker 2>basic signs of normal development.

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<v Speaker 1>So here's your babies in four D. And as we

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<v Speaker 1>can see the identical.

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<v Speaker 2>The sonographer sees a single placenta, a sure sign that

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<v Speaker 2>the twins are identical.

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<v Speaker 1>We can see here a single percenter like a T section,

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<v Speaker 1>in which proves that you're having identical twins. So when

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00:27:31.519 --> 00:27:34.559
<v Speaker 1>would you see them start interacting or reacting against each other.

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<v Speaker 1>We can see them almost sort of moving.

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<v Speaker 2>From now on, the mother will be monitored closely twin

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<v Speaker 2>pregnancies are more at risk of premature births. Immature development

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<v Speaker 2>of lungs and organs can lead to complications. These complications

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00:27:57.440 --> 00:28:02.200
<v Speaker 2>make natural childbirth more dangerous. As a result, twins are

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00:28:02.240 --> 00:28:05.200
<v Speaker 2>around fifty percent more likely to be borne by cesarean

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00:28:05.319 --> 00:28:16.559
<v Speaker 2>section than Singleton's. The timing of the scan also marks

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00:28:16.599 --> 00:28:22.960
<v Speaker 2>the start of the second trimester. The second trimester, from

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<v Speaker 2>twelve to twenty four weeks, will see not only dramatic growth,

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00:28:27.160 --> 00:28:30.000
<v Speaker 2>but massive development in everything from the structure of the

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00:28:30.039 --> 00:28:37.599
<v Speaker 2>brain to the refinement of facial features. By the end

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<v Speaker 2>of this stage, the fetuses will be small but almost

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00:28:41.200 --> 00:28:52.039
<v Speaker 2>perfectly formed. They look very similar, but newer search reveals

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<v Speaker 2>that even at this early stage, identical twins may already

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<v Speaker 2>be less identical. Subtle changes are under way that will

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00:29:02.559 --> 00:29:10.599
<v Speaker 2>become greater throughout their lives, and the mechanism responsible is

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00:29:10.640 --> 00:29:14.279
<v Speaker 2>one of the most complex yet fascinating processes in the

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00:29:14.319 --> 00:29:32.799
<v Speaker 2>whole of human development. Fifteen weeks into their journey from

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00:29:32.839 --> 00:29:36.640
<v Speaker 2>conception to birth, our identical twins begin to move for

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00:29:36.720 --> 00:29:45.680
<v Speaker 2>the first time. They start to interact, exploring their environment

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00:29:45.759 --> 00:29:49.640
<v Speaker 2>with their hands and feet, touching and even appearing to

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00:29:49.759 --> 00:29:59.960
<v Speaker 2>kiss their mother. In later pregnancy will feel the same case.

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<v Speaker 2>Each twin feels in muteroe. At times they appear aggressive,

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<v Speaker 2>at others almost caring. They look identical, but unseen influences

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00:30:15.240 --> 00:30:19.440
<v Speaker 2>may already be taking effect, ones that could subtly alter

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00:30:19.519 --> 00:30:31.920
<v Speaker 2>the expression of genes in their growing body identicals. Jake

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00:30:31.960 --> 00:30:38.079
<v Speaker 2>and Tom are now aged seventeen months. Jake is eight

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00:30:38.200 --> 00:30:46.759
<v Speaker 2>centimeters taller than Tom and four kilos heavier When they

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00:30:46.799 --> 00:30:50.400
<v Speaker 2>were born in two thousand and six, doctors attributed these

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00:30:50.400 --> 00:30:54.680
<v Speaker 2>discrepancies in size and weight to restricted nutrition or blood

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00:30:54.680 --> 00:30:59.079
<v Speaker 2>flow in the womb. They expected Tom to catch up,

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00:31:00.079 --> 00:31:03.200
<v Speaker 2>but after a year and a half, they're investigating whether

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00:31:03.279 --> 00:31:06.680
<v Speaker 2>Tom may be suffering from a genetic condition called Russell's

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<v Speaker 2>Silver syndrome, a growth disorder. One of the causes of

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00:31:12.960 --> 00:31:15.839
<v Speaker 2>this syndrome may be a problem with a growth gene

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<v Speaker 2>on chromosome eleven. Scientists are puzzling over why Tom and

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00:31:22.039 --> 00:31:27.640
<v Speaker 2>his brother do not both have a syndrome. Identical twins,

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00:31:27.680 --> 00:31:39.319
<v Speaker 2>after all, have identical genes. Genetic puzzles like these are

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<v Speaker 2>opening up a little known world at the outer reaches

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00:31:42.400 --> 00:31:51.359
<v Speaker 2>of science, epigenetics. This growing field of biology may help

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00:31:51.440 --> 00:32:00.240
<v Speaker 2>explain the differences between twins like Tom and Jake. Epigenetic

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00:32:00.440 --> 00:32:03.119
<v Speaker 2>reveals that while their DNA code may be the same,

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00:32:04.000 --> 00:32:10.039
<v Speaker 2>the way it functions can differ. The human genome contains

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00:32:10.079 --> 00:32:14.759
<v Speaker 2>around twenty five thousand genes, each with its own specific function,

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00:32:15.400 --> 00:32:21.000
<v Speaker 2>such as producing energy or directing cell division. Now geneticists

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00:32:21.079 --> 00:32:24.960
<v Speaker 2>are investigating a previously unknown aspect of the genome called

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00:32:25.000 --> 00:32:30.160
<v Speaker 2>the epigenome. There is a series of chemicals that act

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00:32:30.200 --> 00:32:37.319
<v Speaker 2>as switches capable of activating or deactivating individual genes. One

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00:32:37.319 --> 00:32:41.079
<v Speaker 2>of these switches works by a process called DNA methylation.

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00:32:43.279 --> 00:32:47.680
<v Speaker 2>This causes enzymes insider cell to attach a minuscule molecular

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00:32:47.720 --> 00:32:52.400
<v Speaker 2>compound a methyl group, to a gene. This compound can

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00:32:52.440 --> 00:32:56.200
<v Speaker 2>deactivate or at times activate the gene, but the gene

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00:32:56.240 --> 00:33:06.400
<v Speaker 2>remains the cell's DNA profile is unchaeed changed. This could

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00:33:06.480 --> 00:33:11.519
<v Speaker 2>explain the difference between identical twins Jake and Tom. Some

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00:33:11.680 --> 00:33:16.039
<v Speaker 2>as yet unidentified environmental factor in early cell development has

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00:33:16.079 --> 00:33:19.119
<v Speaker 2>caused a methyl group to attach itself to a gene

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00:33:19.160 --> 00:33:23.359
<v Speaker 2>on one of Tom's chromosomes, a gene associated with growth.

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<v Speaker 2>The growth gene is still there, but it's been switched off.

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00:33:32.480 --> 00:33:35.480
<v Speaker 2>By investigating the mystery of twins like Tom and Jake,

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<v Speaker 2>Geneticists are finally beginning to find clues to some of

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00:33:39.480 --> 00:33:54.079
<v Speaker 2>the great mysteries of the human genome. This is a

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00:33:54.119 --> 00:33:57.720
<v Speaker 2>map of chromosomes belonging to identical twins from age three

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00:33:57.759 --> 00:34:00.640
<v Speaker 2>on the left to twins aged fifteen on the right.

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<v Speaker 2>The red markings are an indication of the increase in

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00:34:05.000 --> 00:34:08.079
<v Speaker 2>the methylation that has occurred to their chromosomes over half

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00:34:08.119 --> 00:34:12.800
<v Speaker 2>a century. We know that factors like smoking, diet, and

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00:34:12.880 --> 00:34:16.800
<v Speaker 2>chemical exposure can, over a lifetime, wreak havoc with how

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00:34:16.880 --> 00:34:22.039
<v Speaker 2>genes operate. What's astounding is that there are different environmental

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00:34:22.039 --> 00:34:28.079
<v Speaker 2>influences in not only our lifetime, but also in utero. Hormones, space,

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00:34:28.840 --> 00:34:36.079
<v Speaker 2>quality of nutrition can all affect identical embryos differently, even

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<v Speaker 2>those sharing a placenta. The activation and deactivation of genes

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00:34:41.079 --> 00:34:44.400
<v Speaker 2>during early development could explain many of the twists of

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00:34:44.440 --> 00:34:48.079
<v Speaker 2>fate that affect us all why one person is struck

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00:34:48.119 --> 00:34:52.840
<v Speaker 2>by disease while another spared. Epigenetics may also play a

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00:34:52.880 --> 00:34:59.119
<v Speaker 2>significant role in determining sexuality. If sexual preference is associated

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00:34:59.320 --> 00:35:03.159
<v Speaker 2>with an asthet unidentified gene, it may be that the

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00:35:03.199 --> 00:35:08.159
<v Speaker 2>epigenetic suppression or activation of this gene dictates sexual preference.

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<v Speaker 2>These genetic switches may be the answer to why one

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00:35:15.400 --> 00:35:19.400
<v Speaker 2>twin absorbs more testosterone than the other, resulting in one

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00:35:19.480 --> 00:35:25.400
<v Speaker 2>being gay and the other straight. It's becoming clear that

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00:35:25.440 --> 00:35:29.440
<v Speaker 2>our health, personality, tastes, and even appearance are not the

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00:35:29.480 --> 00:35:32.800
<v Speaker 2>product of either our genes or our environment, but that

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00:35:32.920 --> 00:35:38.599
<v Speaker 2>nature and nurture are inextricably bound, with epigenetics the tangible

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00:35:38.639 --> 00:35:46.000
<v Speaker 2>biological link between the two, and most surprisingly of all,

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<v Speaker 2>new research claims these subtle changes to a gene's expression

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00:35:51.079 --> 00:35:54.800
<v Speaker 2>can be passed on down through the generations without affecting

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00:35:54.800 --> 00:36:01.199
<v Speaker 2>the underlying DNA. Studying a register of births and deaths

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00:36:01.559 --> 00:36:05.760
<v Speaker 2>in a remote region of northern Sweden, researchers noticed a

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00:36:05.800 --> 00:36:11.400
<v Speaker 2>peculiar phenomenon. A generation of boys who experienced a famine

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00:36:11.760 --> 00:36:20.679
<v Speaker 2>had grandchildren who led longer lives. On the other hand,

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00:36:21.159 --> 00:36:24.400
<v Speaker 2>descendants of those boys who enjoyed plentiful food as children

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00:36:25.039 --> 00:36:30.199
<v Speaker 2>experienced an increased risk of diabetes, cardiovascular disease, and higher

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00:36:30.280 --> 00:36:38.320
<v Speaker 2>mortality rates. The effect of famine was especially strong if

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<v Speaker 2>the boy was at the age when he was just

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00:36:40.079 --> 00:36:47.119
<v Speaker 2>about to start producing reproductive cells his sperm. It seems

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00:36:47.199 --> 00:36:50.960
<v Speaker 2>the genetic makeup of these reproductive cells were directly but

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00:36:51.079 --> 00:36:56.960
<v Speaker 2>subtly altered by the famine or feast. Through their sperm,

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00:36:57.280 --> 00:37:03.679
<v Speaker 2>they passed on a nutritional legacy to future generations. The

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<v Speaker 2>more we explore the hidden world of epigenetics, the more

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<v Speaker 2>it seems we are not simply a product of our genes.

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<v Speaker 2>We may even have the power to steer our genetic

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00:37:15.239 --> 00:37:19.719
<v Speaker 2>destiny and perhaps that of our descendants, through lifestyle choices

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00:37:20.119 --> 00:37:27.360
<v Speaker 2>such as smoking, diet, and exercise. What makes identicals unique

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00:37:27.440 --> 00:37:31.119
<v Speaker 2>and useful to genetics is that their genome is one

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00:37:31.159 --> 00:37:38.960
<v Speaker 2>hundred percent match, or at least that's what we thought. Now,

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<v Speaker 2>powerful new DNA techniques are revealing a different story, one

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00:37:43.920 --> 00:37:52.000
<v Speaker 2>that is only just unfolding. As the second trimester draws

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00:37:52.000 --> 00:37:54.920
<v Speaker 2>to a close, the twins will have a second scan.

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<v Speaker 2>The development of external features such as limbs and eyes

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00:38:00.280 --> 00:38:03.280
<v Speaker 2>will be checked, and the major organs will be examined

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00:38:03.320 --> 00:38:10.920
<v Speaker 2>for signs of defects. The twins are about twenty centimeters long,

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00:38:11.679 --> 00:38:14.039
<v Speaker 2>small enough to cradle in the palm of the hand.

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<v Speaker 2>The twenty week scan is the time when most mothers

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00:38:23.840 --> 00:38:26.360
<v Speaker 2>will discover whether they're having a boy or a girl.

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<v Speaker 2>Gender identification can be done as early as eleven to

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<v Speaker 2>twelve weeks, but is more certain at the four months scan.

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<v Speaker 2>The scan reveals our twins are boys. Our twins are

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00:38:50.159 --> 00:38:59.760
<v Speaker 2>twenty four weeks into development. Their mother can now feel

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00:38:59.760 --> 00:39:09.559
<v Speaker 2>them kick inside the wound. A battle for space is raging.

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<v Speaker 2>A scan reveals this struggle and perhaps even a glimpse

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00:39:14.199 --> 00:39:23.119
<v Speaker 2>of emerging personalities. Ultrasound studies combined with observations of twins

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00:39:23.159 --> 00:39:28.079
<v Speaker 2>after birth, show very early forms of shy or extrovert behavior.

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00:39:31.039 --> 00:39:34.800
<v Speaker 2>In one study of fraternal twins, the shire twin would

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00:39:34.840 --> 00:39:38.239
<v Speaker 2>occasionally hang onto his umbilical cord and even appear to

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00:39:38.280 --> 00:39:42.800
<v Speaker 2>lick it, while his sister would seek to grab, kick,

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00:39:42.960 --> 00:39:51.320
<v Speaker 2>and push him. Intriguingly, this pattern continued after birth. At

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00:39:51.320 --> 00:39:55.800
<v Speaker 2>four years of age, the shy twin still exhibited retiring behavior,

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00:39:56.679 --> 00:39:59.639
<v Speaker 2>while his more extrovert sister would try to grab and

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00:39:59.679 --> 00:40:05.199
<v Speaker 2>play with him. It seems our personalities may well begin

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00:40:05.280 --> 00:40:21.840
<v Speaker 2>to form in the womb. From week twenty nine onwards,

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00:40:22.239 --> 00:40:31.119
<v Speaker 2>the fetuses are beginning to resemble newborn babies. Their body

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00:40:31.159 --> 00:40:36.280
<v Speaker 2>fat rapidly increases, bones are fully developed but still soft

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00:40:36.320 --> 00:40:50.599
<v Speaker 2>and pliable. Head hair grows thicker, and fingernails reach the fingertips. Already,

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00:40:50.760 --> 00:40:57.559
<v Speaker 2>our twins' fingerprints are different. Epigenetic changes have already impacted

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00:40:57.559 --> 00:41:01.400
<v Speaker 2>the genes that control the pattern of the fingertips. These

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00:41:01.400 --> 00:41:06.960
<v Speaker 2>fingerprint differences will become more pronounced as the fingertips develop.

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00:41:07.360 --> 00:41:11.239
<v Speaker 2>They receive blood from the veins. This makes them swell,

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00:41:11.920 --> 00:41:17.000
<v Speaker 2>forming distinctive fingerprint patterns. If blood flow from the percenter

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00:41:17.079 --> 00:41:20.719
<v Speaker 2>in one twin is restricted, blood may be directed away

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00:41:20.760 --> 00:41:24.679
<v Speaker 2>from the fingers and other extremities, leaving this twin with

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00:41:24.800 --> 00:41:29.440
<v Speaker 2>more wells on their fingerprints than the other. Our fingerprint

401
00:41:29.480 --> 00:41:32.719
<v Speaker 2>patterns can help to indicate how unhealthy our heart will

402
00:41:32.760 --> 00:41:37.440
<v Speaker 2>be in adult life. The more wells, the greater the

403
00:41:37.559 --> 00:41:49.039
<v Speaker 2>chance of later heart problems. From the moment a fertilized

404
00:41:49.039 --> 00:41:52.880
<v Speaker 2>egg divides in two, various influences on the genetic code

405
00:41:52.920 --> 00:41:59.679
<v Speaker 2>conspire to create differences between identical twins, differences that can

406
00:41:59.719 --> 00:42:05.239
<v Speaker 2>become more pronounced over time. Yet it's always been assumed

407
00:42:05.559 --> 00:42:12.119
<v Speaker 2>that identical twins share identical DNA until a discovery in

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00:42:12.159 --> 00:42:19.360
<v Speaker 2>two thousand and seven surprised the scientific world. Researchers set

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00:42:19.360 --> 00:42:22.079
<v Speaker 2>out to investigate one of the most puzzling anomalies in

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00:42:22.119 --> 00:42:26.559
<v Speaker 2>the life of twins, why one succumbs to a genetically

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00:42:26.559 --> 00:42:38.039
<v Speaker 2>inherited disease while the other is unaffected. They chose Parkinson's

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00:42:38.440 --> 00:42:41.159
<v Speaker 2>because it's more likely to be caused by a spontaneous

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00:42:41.199 --> 00:42:49.639
<v Speaker 2>genetic cause than be inherited. So the scientists examined the

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00:42:49.679 --> 00:42:53.880
<v Speaker 2>genes of nineteen pairs of identical twins, including nine pairs

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00:42:53.920 --> 00:42:56.960
<v Speaker 2>in which only one twin showed signs of the genetic disorder.

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00:43:02.719 --> 00:43:06.519
<v Speaker 2>They wanted to challenge the common perception that identicals are

417
00:43:06.559 --> 00:43:12.239
<v Speaker 2>genetically identical. Indeed, their analysis showed that there were differences

418
00:43:12.280 --> 00:43:18.599
<v Speaker 2>between the number of genes each twin had. Genes usually

419
00:43:18.599 --> 00:43:23.440
<v Speaker 2>occur in two copies, one inherited from each parent, but

420
00:43:23.559 --> 00:43:26.639
<v Speaker 2>this study has revealed it's possible to have just one copy,

421
00:43:27.400 --> 00:43:33.480
<v Speaker 2>or to have three or more copies of the same gene.

422
00:43:33.760 --> 00:43:38.519
<v Speaker 2>This phenomenon, called copy number variation, can fundamentally alter the

423
00:43:38.559 --> 00:43:42.119
<v Speaker 2>genes function and may induce the disease in one twin

424
00:43:42.320 --> 00:43:58.159
<v Speaker 2>and not the other. It's a major breakthrough in our

425
00:43:58.280 --> 00:44:03.639
<v Speaker 2>understanding of disease and in the study of twins, because

426
00:44:03.679 --> 00:44:07.440
<v Speaker 2>the discovery means that identicals are not a one hundred

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00:44:07.480 --> 00:44:12.679
<v Speaker 2>percent genetic match. The very definition of identical twins needs

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00:44:12.719 --> 00:44:16.039
<v Speaker 2>to be revised, as advances in technology can prove that

429
00:44:16.119 --> 00:44:20.039
<v Speaker 2>small but significant changes are present in all identical twins.

430
00:44:24.719 --> 00:44:29.079
<v Speaker 2>Our identical twin boys are approaching full urn already. There

431
00:44:29.079 --> 00:44:32.440
<v Speaker 2>will be subtle genetic differences between them that may shape

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00:44:32.639 --> 00:44:38.960
<v Speaker 2>very different futures. But first they must face the most

433
00:44:39.039 --> 00:44:42.920
<v Speaker 2>dangerous stage of their long journey in the womb, the birth.

434
00:44:47.840 --> 00:44:57.679
<v Speaker 2>It's thirty five weeks. The twins are now fully developed.

435
00:45:01.960 --> 00:45:06.559
<v Speaker 2>They have hair, eyelashes, nails, and can open and close

436
00:45:06.599 --> 00:45:14.280
<v Speaker 2>their eyes and mouths. Conditions in the womb are becoming cramped,

437
00:45:15.000 --> 00:45:18.639
<v Speaker 2>but around two kilos each weighs about a third less

438
00:45:18.639 --> 00:45:28.719
<v Speaker 2>than the average singleton baby, but combined they put tremendous

439
00:45:28.760 --> 00:45:35.480
<v Speaker 2>pressure on the womb. Premature deliveries for twins before full

440
00:45:35.599 --> 00:45:47.440
<v Speaker 2>term at thirty seven weeks are common. Our twins will

441
00:45:47.480 --> 00:45:52.719
<v Speaker 2>be borne at week thirty five by cesarean section. About

442
00:45:52.719 --> 00:45:55.280
<v Speaker 2>half of twins are delivered this way due to the

443
00:45:55.280 --> 00:45:58.639
<v Speaker 2>difficulties and dangers of giving birth to two babies naturally.

444
00:46:03.119 --> 00:46:06.480
<v Speaker 2>To ensure safety, there is a larger than normal delivery

445
00:46:06.519 --> 00:46:20.159
<v Speaker 2>team on hand. The obstetrician swiftly cuts the first membrane

446
00:46:20.800 --> 00:46:28.920
<v Speaker 2>and then the second Caesareans are always performed quickly to

447
00:46:29.000 --> 00:46:36.199
<v Speaker 2>reduce the risks of complications. He plunges his hand into

448
00:46:36.199 --> 00:46:45.199
<v Speaker 2>the womb and takes the first baby out. The baby

449
00:46:45.280 --> 00:46:52.840
<v Speaker 2>takes his first breath and emits a healthy screen. The

450
00:46:52.920 --> 00:46:56.480
<v Speaker 2>cord to the placenta, his lifeline for the last thirty

451
00:46:56.519 --> 00:47:13.400
<v Speaker 2>five weeks is finally cut. Working briskly, the surgeon looks

452
00:47:13.440 --> 00:47:19.239
<v Speaker 2>for his twin. With his twin brother out of the way,

453
00:47:19.639 --> 00:47:32.760
<v Speaker 2>he follows quickly, also paid first. Following birth. It's not

454
00:47:32.840 --> 00:47:36.519
<v Speaker 2>always obvious to the obstetrician whether the twins are identical

455
00:47:36.719 --> 00:47:42.559
<v Speaker 2>or fraternal. Our twins have a shared placenter, the clearest

456
00:47:42.599 --> 00:47:49.239
<v Speaker 2>indication that they are identical. If the identicals have separate percenters,

457
00:47:49.400 --> 00:47:54.039
<v Speaker 2>as happens occasionally, DNA analysis is the only sure method

458
00:47:54.039 --> 00:48:10.440
<v Speaker 2>of identification. After an extraordinary journey, our two reproductive marvels

459
00:48:10.760 --> 00:48:15.159
<v Speaker 2>have made it safely into the world. They may look alike,

460
00:48:15.880 --> 00:48:25.119
<v Speaker 2>but we now know they are already different. Two hundred

461
00:48:25.159 --> 00:48:29.760
<v Speaker 2>and forty five days ago, a fertilized egg divided, creating

462
00:48:29.840 --> 00:48:36.639
<v Speaker 2>two identical embryos. From that moment onwards, their paths began

463
00:48:36.719 --> 00:48:44.800
<v Speaker 2>to diverge. Inequalities in nutrition or space, differing exposure to hormones,

464
00:48:46.400 --> 00:48:52.119
<v Speaker 2>small alterations in their epigenetic profiling, even minute differences in

465
00:48:52.159 --> 00:48:58.599
<v Speaker 2>the underlying genome, all combined to create subtle, yet significant differences.

466
00:49:00.000 --> 00:49:04.599
<v Speaker 2>Now the twins are about to embark on the next

467
00:49:04.599 --> 00:49:09.840
<v Speaker 2>stage of their journey. As they grow, facing diverse experiences

468
00:49:09.840 --> 00:49:14.000
<v Speaker 2>and influences, the differences between them will become ever greater.

469
00:49:18.519 --> 00:49:22.039
<v Speaker 2>These differences bring us closer to answering some of humanity's

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00:49:22.079 --> 00:49:27.400
<v Speaker 2>most profound questions. The study of identical twins has shed

471
00:49:27.440 --> 00:49:30.559
<v Speaker 2>new light on the complex mix of genetics and environment,

472
00:49:31.079 --> 00:49:37.239
<v Speaker 2>nature and nurture that makes each of us unique. It

473
00:49:37.320 --> 00:49:41.519
<v Speaker 2>has profound and far reaching implications for how we all

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00:49:41.719 --> 00:49:42.599
<v Speaker 2>lead our lives.