Sex of the baby:

Parents often will be curious to know whether their new baby will be a boy or a girl.  But there is no simple way for them to find this out before the baby is born.

Parents usually just have to wait.  The sperm carries the gene that determines the sex of the baby.  And it is determined one way or the other (male or female) at  the moment the sperm joins  the  egg  once  and  for  all.   A man probably has  the same number of sperms with genes for girls as he has sperms with genes for boys.   But that does not mean that half the children in each family will be girls and half boys.

We all know families with only girls or only boys.  By chance, the fertilizing sperms have always been sperms for the same sex.  This could happen in any family, but most large families do have some boys and some girls.  It is all a chance and nobody can do anything about it.