Human Growth and Development / Unit 2 HGD 0182 short lesson, about 20 seconds
Fraternal and Identical Twins
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The idea
Dizygotic, or fraternal, twins come from two eggs fertilised at once; monozygotic, or identical, twins come from one zygote that splits.
In practice
Identical twins arising naturally in about zero point four percent of pregnancies.
Where people slip
In vitro fertilization raises the chance of identical twins, to between about one and a half and five and a half percent.
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