Term 3 Science
ACE
Formation of twins
Updated 2012
Copyright Ng Wei Kai (2i1 16)
Fertilisation
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Before we learn more about twin conception, let
us first understand how single babies are formed
via fertilisation.
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A single ovum is released once every month from
a woman’s ovaries during the ovulation stage of
the menstrual cycle.
Fertilsation
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The ovum then travels to the uterus via the
fallopian tube.
During this period, sperms from males swim up the
fallopian tube to mate with the ovum.
The male and female gametes fuse to form a
zygote, restoring the diploid number of
chromosomes
Fertilisation
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After fertilisation, the zygote goes through mitotic
cell division known as cleavage.
Many cells are then formed from the cytoplasm of
the zygote
This ball of cells is called a blastocyst
The blastocyst then embeds itself in the uterine
lining
Fertilisation
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Upon implantation, the developing baby is called
an embryo.
After 9 months of development, it will become a
fetus.
During this period, it is protected by the amniotic
sac, which is filled with amniotic fluid.
Supplied nourishment and oxygen and removed
of waste via the umbilical chord and placenta.
Twin conception
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1.
2.
Now that we understand how single babies are
formed, let us move on to the conception of twins.
Two types of twins:
Identical (monozygotic)
Fraternal (dizygotic)
Fraternal twins
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Two-thirds of all twins are dizygotic
occur when two sperm fertilize two distinct eggs. In
this instance, rather than releasing one egg during
ovulation, the mother has released two.
Fraternal twins
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Fertilisation of two separate ovum results in two
distinct embryos.
However, if these embryos implant very near to
each other along the endometrium, the two
placentas can become fused.
Genetically similar, not identical
Multiples births
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Multiple births can also be carried out using this
process if more eggs are released
For example, if three eggs are released and
fertilsed, the children born would be known as
trizygotic triplets.
Interesting fact!
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Nadya Suleman from Bellflower, California gave
birth to 6 males and 2 females, who were
conceived via In-vitro fertilisation, on January 26,
2009
They are fraternal since they have different
genders.
Identical twins
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Occurs when one sperm fertilises one egg
Instead of having the blastocyst remaining as one
cell group, it splits in two.
The two balls of cells then develop into two
different embryos.
Identical twins
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Since the twins come from the same fertilsed egg,
they will share identical features such as same
gender.
Bibliography
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[Untitled image of fraternal twins]. Retrieved 17 August 2012, from :
http://i.dailymail.co.uk/i/pix/2009/09/26/article-1216253-069872FB000005DC530_468x317.jpg
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[Untitled image of gestation] . Retrieved 17 August 2012, from : http://staticwww.icr.org/i/articles/af/made_in_his_image_gestation_wide.jpg
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[Untitled image of identical twins]. Retrieved 17 August 2012, from:
http://www.mombaby.org/UserFiles/File/TTTS_images/TTTS01.jpg
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[Untitled image of fertilsation]. Retrieved 17 August 2012, from:
http://msnbcmedia4.msn.com/j/MSNBC/Components/Photo/_new/tdy090521-twingraphic-6a.grid-6x2.jpg
Bibliography
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[Untitled image of the Suleman octoplets]. Retrieved 17 August 2012, from:
http://spilldabeanz.com/wp-content/uploads/2012/06/octomom6.jpg
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[Untitled image of blastocyst]. Retrieved 17 August 2012, from:
http://4menandalittlebaby.files.wordpress.com/2011/03/blastocyst.jpg
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Twins. (n.d.). Retrieved 15 August, 2012 from wikipedia:
http://en.wikipedia.org/wiki/Twin
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Neer, K. (n.d.). Howstuffworks.com. Retrieved from
http://science.howstuffworks.com/environmental/life/genetic/twin.htm