How do twins happen?
In: Biology
Dizyotic (fraternal) twins: The ovaries somehow release two eggs instead of one. Both eggs are fertilized by two sperm cells and then both zygotes are implanted in the uterus.
Monozygotic (identical) twins: Only one egg and sperm. Some time very early in the pregnancy the zygote somehow eplits into two, making two identical zygotes which develop into two identical embryos.
Fraternal twins happen when 1 zygote splits into 2 of them and 1 sperm goes into each of them which causes them to fertilize simultaneously. Identitcal twins happen when 2 sperms instead of 1 sperm make it inside 1 zygote which causes them to fertelize simultaneously in the same egg.
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