Using the Hardy-Weinberg Theorem
Step 1 - Calculate the Allele Frequencies

Genotype    Individuals     “M” Alleles    “N” Alleles     Total  Alleles
MM                 80                    160                     0                    160
MN                  80                      80                   80                    160
NN                   40                        0                   80                      80 
Totals            200                    240                 160                   400

Allele Frequency           M” 240/400    “N” 160/400
                                             = 0.60             = 0.40

Step 2 - Calculate the Expected Frequencies

    p2 + 2pq + q2 =1

(0.6)2 + 2(0.6X0.4) + (0.4)2 = 1
0.36   +        0.48     +  0.16= 1

Step 3 - Compare Expected and Observed Frequencies

Using the Hardy-Weinberg Theoremsing the Hardy-Weinberg TheoremGenotype           Expected Frequency          Observed Frequency
MM                            0.36                               160/400=0.40
MN(NM)                   0.48                               160/400=0.40
NN                             0.16                                 80/400=0.20