@elam84 In humans there is a slight prenatal bias toward males at about 51.3% (source below). So, with some basic probability. The chance of two boys is 0.513 * 0.513 * 100 = 26.32%. The chance of two girls is 0.487 * 0.487 * 100 = 23.72%. And the chance of mixed sibs is 0.487 * 0.513 * 2 * 100...