According to a simple genetic principle, if both the mother and the father of a child have genotype Aa, then there is probability 1/4 that the child will have genotype AA; there is probability 1/2 that it will have genotype Aa; and there is probability 1/4 that it will have genotype aa. In a random sample of 24 children having both parents with genotype Aa, it is found that 10 have genotype AA, 10 have genotype Aa, and 4 have genotype aa. Investigate whether the simple genetic principle is correct by carrying out a X2 test of goodness-of-fit.