The 1:1 ratio results from the way the X and Y chromosomes are doled out in sperm and eggs. We know that boys and girls are produced in much the same frequency. But how – and why – is this 1:1 ...

transcript Parker Finn narrates a sequence from “Smile 2,” starring Naomi Scott. “Hi, I’m Parker Finn. I am the writer, director and one of the producers of “Smile 2.” This scene takes ...