This document discusses identical and non-identical twins. Identical twins come from a single fertilized egg that splits into two, so they are genetically identical. Non-identical twins develop from two separate eggs fertilized by two separate sperm, so they are no more genetically similar than normal siblings. Around one in three sets of twins are identical, while the other two-thirds are non-identical. Identical twins are always the same sex while non-identical twins can be either the same or opposite sex.

1. TWITWINSNS

2. IdenticalIdentical andand
non-non-
identicalidentical
• Non identicalNon identical identical

3. ,, and Identical twins form when one egg has beenand Identical twins form when one egg has been
fertilised by one sperm and the zygote splits intofertilised by one sperm and the zygote splits into
two. This happens at the very earliest stage oftwo. This happens at the very earliest stage of
development, when the zygote is no more than adevelopment, when the zygote is no more than a
cluster of a few cells. Dividing this early incluster of a few cells. Dividing this early in
conception means that each baby has exactly theconception means that each baby has exactly the
same genetic information as the other.same genetic information as the other.
Identical twins can also occur when one a womanIdentical twins can also occur when one a woman
has undergone fertility assistance and has hadhas undergone fertility assistance and has had
one fertilised egg returned to her uterus.one fertilised egg returned to her uterus.
IDENTICALIDENTICAL
TWINSTWINS

4. • If this egg then splits into two, anIf this egg then splits into two, an
identical twin pregnancy can result.identical twin pregnancy can result.
• Identical twins are not dependent on race,Identical twins are not dependent on race,
country or ethnicity. The odds of havingcountry or ethnicity. The odds of having
identical twins are the same for everyidentical twins are the same for every
couple, in every pregnancy, wherever theycouple, in every pregnancy, wherever they
live in the world.live in the world.
• Around one in every three sets of twinsAround one in every three sets of twins
born is identical, and the remaining 2/3 isborn is identical, and the remaining 2/3 is
of the non-identical varietyof the non-identical variety..

5. NON-IDENTICALNON-IDENTICAL
TIWNSTIWNS
• Non-identical twins are uniquely separateNon-identical twins are uniquely separate
individuals who just happen to beindividuals who just happen to be
gestating at the same time and place asgestating at the same time and place as
each other. Non-identical twins form fromeach other. Non-identical twins form from
two completely separate eggs which aretwo completely separate eggs which are
fertilised by two completely separatefertilised by two completely separate
sperm. These fraternal twins are no moresperm. These fraternal twins are no more
alike than any other siblings in a familyalike than any other siblings in a family
with the same biological mother andwith the same biological mother and
father.father.

6. • Some people still believe that theSome people still believe that the
incidence of having twins skips aincidence of having twins skips a
generation but this is not true.generation but this is not true.
• Because identical twins share the sameBecause identical twins share the same
genes, they are always the samegenes, they are always the same
gender. But non-identical twins may begender. But non-identical twins may be
the same gender or the oppositethe same gender or the opposite
because they only share 50% of thebecause they only share 50% of the
same genetic coding.same genetic coding.

7. Sometimes, twins haveSometimes, twins have
problems, for example someproblems, for example some
times they born togethertimes they born together

9. jokejoke
That funny moment when you seeThat funny moment when you see
two twins arguing and one says totwo twins arguing and one says to
the otherthe other
-- uglyugly

10. Ja ja ja ja ja ja jaJa ja ja ja ja ja ja
jaja

11. AND THIS IS OURAND THIS IS OUR
PRESENTATIONPRESENTATION
FOR NOWFOR NOW