Semi-identical twins?

Miriam tells us in THE DEADLIEST LIE that her servant Phoebe was a Greek foundling her mother rescued. Finding the infant wrapped in a soiled blanket in the Bruchium Quarter when she was hardly more than a day old, her mother brought the baby home and hired a wet nurse for her first three years.

In the newest and fifth book in the Miriam bat Isaac Mystery Series, THE DEADLIEST THIEF, we learn that unbeknownst to Phoebe, she had an identical twin. Unable to provide for both girls, their parents abandoned one (see my blog of March 12, 2019) with the hope that a wealthy woman would find and adopt her.

No doubt you’ve heard of identical and fraternal twins. Identical twins come from a single fertilized egg that splits and develops into two embryos. Fraternal twins (see my blog of March 27, 2018) develop from two fertilized eggs that implant in the womb. Consequently, identical twins have the same genes and gender, whereas fraternal twins have only about 50% of their genes in common and can develop into a girl and a boy.

But in 2007, scientists identified a third type of twins called semi-identical twins. Here, during that first cell division when the fertilized egg splits into two embryos, the chromosomes do not duplicate or assort equally. So, the twins are no longer identical. In fact, they can develop into two different genders. So far, only two cases of semi-identical twins have been recorded.

But in THE DEADLIEST THIEF, Phoebe and her sister are so identical that you and Miriam might not be able to tell the difference even with my hint. Need another? Okay, click here.