Monozygotic twins, or identical twins. result from the fertilization of a single egg with a single sperm. Fraternal twins, or dizygotic twins, are the product of fertilization of two different eggs.
In identical twins, as the cells divide and multiply, at some point very early in the embryonic growth, they spit into two individuals. As you can imagine, the genetic material in these twins is identical, hence the name identical twins. Monozygotic twins are always the same sex (except in my dark fantasy Gemini Rising!)
Fraternal twins, can be different genders, look different, and have different characteristics. Even though we call identical twins identical and think of their genetic material as identical, we need to keep in mind that there is another important factor—environmental influences—which means identical twins come from the same genetic material, but, in characteristics they may actually have differences as well.
Whose genes produce monozygotic twins? Only women ovulate. So, the mother's genes control this propensity to twins, and the father’s genes don't. This is why having a background of twins in the family matters only if it is on the mother's side.
In vitro fertilization (IVF)
Gemini Rising stars monozygotic twins, Alina and Alain aren't quite your average identical twins, however. As their names suggest, they are male/female twins--which scientifically cannot occur. When they are born, to escape the notoriety and the scientific probing, Lord and Lady Alastair whisk their miracle children to their island castle on an island off the coast of England (the island is fictional but patterned after the beautiful and majestic St. Michael's Mount which is off the coast of England)
Here, Alina and Alain grow up in relative seclusion until they reach their 18th birthday. After so long under the domination of their father, who won't even allow internet in the castle, Alain is ready to leave the Keep for good, but Alina fears being alone without friends to turn to.
Have a wonderful Wednesday!