Most people assume that if twins look very much alike, the twins must be identical. But actually, determining whether or not twins are identical, (or their zygosity) can be a costly proposition. Most people know that fraternal twins are the result of two eggs being fertilized, and that identical twins are the result of one egg that was fertilized and then split. Fraternal twins share no more than 50% of their genes and are no more alike than other siblings in the family. However, identical twins are genetically. . .well, identical. Many times zygosity can be determined simply by looking … Continue reading →