While identical twins are seen more as an accidental splitting of a single egg, there could be a good reason mothers produce non-identical twins from two separate eggs.
Identical twins look the same, are the same sex, share the same birthday and shares the same genes.
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Interestingly, there are more non-identical twins in Australia now than there have been before. The number of twin pregnancies has grown over the past 30 years.
Semi-identical twins share all the DNA passed on from their mother, but only a portion from their father.
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Hannah Brown, South Australian Health & Medical Research Institute
Semi-identical or sesquizygotic twins occur when two sperm fertilise one egg. A boy and a girl in Brisbane are only the second set of semi-identical twins known in the world.
Successfully separating conjoined twins is a complex operation that depends on how they are joined as well as the experience and skill of the surgical team.
Delivering twins is a balance between preventing pregnancy complications and the dangers of prematurity. New research suggests there is an optimum time.
Genes do have an influence over school performance. But they are never the full story.
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Some students struggle because of biological constraints on learning. This can be overcome to an encouraging degree, but only with special and adequate resources.
Identical twins share the same DNA.
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