article_snippet.sent: Either by one sperm fertilizing one egg, which then splits into two foetuses, or by two different sperm fertilizing two different eggs.
article_snippet.sent: The first method leads to monozygotic, or identical twins, who share the same set of DNA, and so will be the same sex and largely share the same physical characteristics.
article_snippet.sent: The first method will create dizygotic, or non-identical twins, who do not share the same genetic material and can therefore be born as different genders and with different physical characteristics.