Question

Identical twins Jan and Fran were very close sisters. So, when Jan died, suddenly Fran moved in to help take care of Jan’s daughter (her niece), Millie. Some time later Fran married her brother-in-law and became Millie’s stepmother. When Fran announced that she was pregnant, poor Millie became confused and curious. “So,” Millie asked, “who is this baby? Will she be my twin? Will she be my sister, my stepsister, my cousin?” Can you answer her questions? What is the genetic relationship between Millie and the baby? What processes are involved in the formation of gametes, and how do they affect genetic variation?

Answer 1

The baby will be Millie's half sister and her first cousin. Because Jan and Fran were identical twins, a genetic fingerprinting can suggest that the baby and Millie were siblings with the same mother and father. This is happened because Fran and Jan would have had identical genetic markers.

Gametes are able to be formed via meiosis which leads to independent assortment of chromosomes. This can ensure that all offspring are not identical and so Millie will not be the twin of the baby.