The gene for curled wings (C/c) is located nearly at the end of the long arm of chromosome 2 of Drosophila, while the gene for smooth abdomen (S/s) is nearly at the end of the short arm of the same chromosome (the centromere is located about 2/3 of the distance along the chromosome). The gene for ebony body (E/e) is near the end of chromosome 3. A true-breeding wild type fly is crossed with a true-breeding fly that has curled wings, smooth abdomen and ebony body (all recessive traits).

(a) Write the genotypes of the parents and the offspring (F1).

(b) Sketch the arrangement of chromosomes 2 and 3 at metaphase of meiosis 1 in the gamete-producing cells of the F1. (Assume no crossing-over).

(c) Sketch all possible combinations of the two chromosomes in the gametes. (Assume no crossing-over).

(d) If the F1 is crossed with a triple recessive fly (known as a backcross), what would be the phenotypes of the progeny (assume no crossing-over). What would you expect their relative numbers to be?

(e) If crossing-over occurred what difference would you expect in the results of the F1 backcross?

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Arrangement of chromosomes 2 and 3 at metaphase of meiosis 1 in the gameteproducing cells of the F1 ... View the full answer