This document discusses genetic differences found in identical twins despite having nearly identical DNA. While twins are considered identical if they come from the same zygote and have the same physical characteristics, studies have found differences in gene expression and environmental factors that make twins unique. Research has shown that although twins have nearly identical genomes, differences can occur in the number of copies of gene segments as well as chemical markings on genes, which can lead to differences in traits and health conditions. Environmental influences like the conditions in the womb, lifestyle choices, and unique life experiences can also impact gene expression and lead to differences between twins.

1. UNDER THE SKIN: GENETIC
DIFFERENCES IN IDENTICAL TWINS
By: Brittany Lynch

2. THESIS
 The distinct differences found at the genetic level in
twins are causing scientists to question the idea of
“identical”.

3. TYPES OF IDENTICAL TWINS
 Dichorionic, Diamniotic
 Monochorionic, Diamniotic
 Monochorionic, Monoamniotic

4. DICHORIONIC, DIAMNIOTIC TWINS
 Zygote split in the first two days after fertilization
 Develop in different placentas and amniotic sacs
 Only occur 20-30% of the time

5. MONOCHORIONIC, DIAMNIOTIC TWINS
 Zygote splits after the first two days of fertilization
 Grow in the same placenta and different amniotic sacs
 Occur most often

6. MONOCHORIONIC, MONOAMNIOTIC TWINS
 Grow in the same placenta and amniotic sac
 Only occur about 1% of the time

7. WHAT IS IDENTICAL?
 To be considered an identical twin:
 have to come from the same zygote
 have same blood type
 have to be the same sex
 have the same hair color

8. JONATHAN MILL
 Study was used to determine how genes are activated
differently in identical twins
 studied the genome of 22 pairs of identical twins
 did have identical DNA, but they had certain differences in chemical
markings
 chemical markings do not alter the DNA sequence, but they do
leave marks on genes

9. NATURE VS. NURTURE
 Genes = Nature
 Environment = Nurture
 Manel Esteller
 studied 49 pairs of identical twins
 determine that epigenetic analysis could differentiate between
twins in a criminal case

10. EVERY BRAIN IS UNIQUE
 Life experience influences brain differences
 change the strength of connections between certain neurons
 Jumping Genes
 genes that paste copies of themselves into the genome
 causes cells to act differently
 can lead to differences in cognitive abilities, personality
traits, and susceptibility to neurological problems

11. TESTS USED TO IDENTIFY DIFFERENCES
 High resolution cameras
 Fingerprinting
 Iris scanners

12. DIFFERENCES DISCOVERED
 Gene Expression
 Environmental Factors

13. GENE EXPRESSION
 Although they did possess nearly identical genomes,
closer study revealed they often differed in the number of
copies of individual gene segments. For instance, one
twin might be missing a segment, or possess more copies
of that segment than the other twin
 They can develop different disorders and illnesses

14. ENVIRONMENTAL FACTORS
 Fingerprints
 caused by the different conditions experienced by the fetuses
in the womb
 Smoking, drugs, and alcohol
 Sun
 Personality Differences
 caused by different chemicals in the body that are affected by
a person’s lifestyle choices

17. WORKS CITED
 http://www.featureshoot.com/wp-content/uploads/2012/01/Eva_Johanna_Gill_0213_F.jpg
 http://api.ning.com/files/w3vIIvgIdO5AAeFt7G93WcNrsN5nS2fCi-74WFDZbP5tfmnnCp5AOx4IDrKz5bPa1B-
QrgSHX25vpBlYsrqHgzYzdm1lzSz4/natgeotwins01.jpg
 http://en.es-static.us/upl/2011/07/twins_twin.jpg
 http://questional.com/images/uploads/34/Identical-Twins-in-the-Womb.jpg
 http://medind.nic.in/ibn/t09/i1/IndianJRadiolImaging_2009_19_1_81_45352_u1.jpg
 http://radiographics.rsna.org/content/29/5/1371/F16.expansion.html
 http://1.bp.blogspot.com/_29vlt4MXQ-
A/S5Z3oYGfMhI/AAAAAAAAB2U/52NonF1w66Q/s400/DichorionicDiamniotic.jpg
 http://static.ddmcdn.com/gif/dna-ch150.jpg
 http://www.genengnews.com/media/images/GENHighlight/April4_2011_3769185_BlueBrainDNA_FiveNewAlzh
eimerGenes2689161031.jpg
 http://www.infobarrel.com/media/image/33385.png
 http://ribomed.com/wp-content/uploads/2011/12/methylmagnetslidev4-copy.jpg
 http://myidentico.com/wordpress/wp-content/uploads/2011/06/10598078-fbi-fd258-fingerprinting.jpg
 http://i.i.com.com/cnwk.1d/i/tim/2011/03/09/helmet_brain_540x405.jpg
 http://scientopia.org/blogs/scicurious/files/2011/05/neurons4.jpg
 http://truthsquad.tv/wp-content/uploads/2010/12/art_illu_biometrics1.jpg
 http://www.buzzle.com/img/articleImages/365107-57010-11.jpg
 http://www.techshout.com/images/nikon-d40x-camera.jpg
 http://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Gene.png/270px-Gene.png
 http://www.bayareaalliance.org/images/e-Environment.jpg
 http://www.broadinstitute.org/files/news/images/2011/chromosome.jpg
 http://topnews.in/health/files/Gene_2.jpg
 http://abcnews.go.com/blogs/headlines/2012/01/a-thing-or-two-about-twins/