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, probability 1/2 that she will have genotype Aa, and probability 1/4 that she 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 four have genotype aa. Investigate whether the simple genetic principle is correct by carrying out a χ2 test of goodness-of-fit.