Why are the chances of an offspring being male or female always 50:50?
The movement of sperm is random.
Equal number of X and Y bearing sperms are released.
The egg has no particular affinity towards a X bearing sperm or a Y bearing sperm
The chances of an offspring being male or female is 50:50 due to several factors. While the movement of sperm is always random, the number of sperm carrying X and Y chromosome respectively is almost equal. This means that both types of sperm have equal chances of fertilizing the egg. All these could have been negated if the egg had an affinity towards a specific type of sperm. Fortunately, the egg has no special affinity for either of the two sperm types, thus allowing the 50:50 ratio between males and females.