1. An ACE project by Bryan Yan 2I102
Twins
An ACE project by Bryan Yan 2I102

2. Agenda Fraternal Twins Identical Twins Semi-Identical Twins
Siamese Twins

3. Fraternal Twins – What? Non-Identical Twins
Small chance of having the same chromosome profile
May be different sex

4. Fraternal – How?
Two eggs are independently fertilized by two different sperm cells
Two fertilized eggs are implanted in the uterus wall at the same time

5. Fraternal Twins – Who? More common for older mothers
Twinning rates doubling in mothers over the age of 35

6. Fraternal Twins - Advances
Advent of technologies and techniques to assist women in getting pregnant has cause the rate of fraternals to increase

7. Identical Twins – What? Nearly genetically identical
Same sex, unless there are mutations during development

8. Identical Twins – How? Single egg is fertilized to form one zygote
Then divides into two separate embryos

9. Identical Twins – When?
Occurs approximately in every 3 out of 1000 births
For IVF, it occurs approximately in every 21 out of 1000 births

10. Semi-Identical Twins – What?
Genetically identical maternal genes
Genetically dissimilar paternal genes

11. Semi-Identical Twins – How? (Type 1)
Polar Twins
A sperm fertilizes the ovum while the other fertilizes the polar body
25% genetic identity

12. Polar Body?
Diploid cells in animals undergoing cytokinesis after meiosis to produce egg cells
Sometimes divide unevenly

13. Polar Body? Most of the cytoplasm is segregated into one ovum
Other smaller cells are called polar bodies

14. Semi-Identical Twins – How? (Type 2)
Sesquizygotic twins
Two sperms fertilize one ovum
Form a triploid
Triploid splits

15. Sesquizygotic twins
Both cells from triploid splitting embeds on the endometrium
Develop into identical twins

16. Siamese Twins – What? Conjoined twins
Twins whose bodies are joined at a certain part e.g. upper chest

17. Siamese Twins – How? A fertilized egg completely separates
But stem cells (which search for similar cells) find like-stem cells on the other twin
Fuse the twins together

18. Siamese Twins – When?
Ranges from 1:50000 births to 1: births depending on country of birth

19. Siamese Twins – Where?
Most common in Southwest Asia and Africa

20. Siamese Twins – Who?
More common amongst females with a 3:1 ratio

21. References http://en.wikipedia.org/wiki/Twin

22. References (Continued)

23. Thank You!