There are 23 pairs of chromosomes in each human cell and the autosomes (chromosome pairs 1-22) determine certain characteristics. However, there is still one more pair of chromosomes and these are called the sex chromosomes and they can either be shaped as XX or XY. The father's chromosome is the chromosome that determines whether it is a boy or girl, and there is an exact 50/50 chance of it being male or female you just need to draw a punnet square.
Hope this helps :)
