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Polar Body Twinning

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Definition: A theorized third type of twinning that occurs when an unfertilized ovum splits into two equal parts and is subsequently fertilized by two separate sperm. Polar body twins share about 75% of their genetic markers, less than identical twins but more than fraternal twins.

Polar Body Twinning is distinguished from semi-identical twinning in that the egg splits before fertilization. Although a case of semi-identical twinning has been confirmed, polar body twinning remains a theory.
Also Known As: half twins, half-identical twinning
Common Misspellings: poler body twinning
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