When two events (call them A and B) are Mutually Exclusive it is impossible for them to happen together: P(A and B) = 0. The probability of A and B together equals 0 (impossible).
Generation Z. Generation Z (also known as The Founders, Post-Millennials, the iGeneration, Plurals or the Homeland Generation) is the demographic cohort after the Millennials.
XX/XY sex chromosomes. The XX/XY sex-determination system is the most familiar, as it is found in humans. The XX/XY system is found in most other mammals, as well as some insects. In this system, most females have two of the same kind of sex chromosome (XX), while most males have two distinct sex chromosomes (XY). The X and Y sex chromosomes are different in shape and size from each other, unlike the rest of the chromosomes , and are sometimes called allosomes.