The fruit fly, Drosophila melanogaster, has autosomal genes for body colour and wing shape. Gene B/b is involved in the production of body colour: • B = dominant allele for brown body colour • b = recessive allele for black body colour. Gene D/d is involved in wing shape: • D = dominant allele for straight wing • d = recessive allele for curved wing. A dihybrid test cross was carried out between flies heterozygous for body colour and for wing shape and flies homozygous recessive for body colour and for wing shape. (a) Table 5.1 shows the number of offspring of each phenotype obtained in the test cross. [Table 5.1]

1. (a)Use Table 5.1 to calculate the expected number of each phenotype if the two genes are on different autosomes. Write your answers in the table.[1]
2. (b)A chi-squared (x2) test was carried out to compare the observed results with the results that would be expected from a dihybrid cross involving genes on different autosomes. The value of x2 = 2097.836. Table 5.2 shows the critical values for the x² distribution. [Table 5.2] Explain how the value of x² and Table 5.2 can be used to assess the significance of the difference between the observed results and the expected numbers in Table 5.1.[4]
3. (c)Suggest explanations for the observed results in Table 5.1.[4]

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