When you use clones from a mother plant you are sure that your plants will turn out to be all female, which is what you want.
However growing from seeds you will have to check regularly if they turn out to be male or female. Unfortunately the male plants develop faster than the female plants and can cause early polination of your plants, which in turn will cause it to grow seeds in your buds of your female plants later on. So make sure you take away those male plants in time, and do it carefully not to loose any pollen in your grow room.
Check the pictures here below how to determine the sex of your plants at the early stages of the growing process.
Very unusual but happens sometimes.
This is a plant that has both sexes.