The genotype of F1 individuals in a tetrahybrid cross is AaBbCcDd. Assuming independent assortment of these four genes, what are the probabilities that F2 offspring will have the following genotypes?

a)aabbccdd
b)AaBbCcDd
c)AABBCCDD
d)AaBBCcDd
e)AaBBCCdd

Please help me on tackling problems like this in a systematic way.