[Science Form 4] Twins

Identical Twins

• Formation: The fertilisation of an ovum by a sperm forms a zygote, which divides into half and produces two embryos.
  
  
• Placenta: Share the same placenta in the mother's uterus.
  
  
• Genetic make-up: Have the same chromosome make-up.
  
  
• Physical appearance: Usually have similar physical appearances.
  
  
• Sex: Are of the same sex.

Non-identical Twins

• Formation: The fertilisation of two ova by two sperms, separately.
  
  
• Placenta: Have separate placentas in the mother's uterus.
  
  
• Genetic make-up: Have separate sets of chromosome make-up.
  
  
• Physical appearance: Usually have different physical appearances.
  
  
• Sex: May be of different sexes or the same sex.