Essential Genetics 6th Edition by Daniel Hartl

Exercise 9

In Drosophila , the dusky mutation is an X-linked recessive that causes small, dark wings. In a stock of wildtype flies, you discover a single male that has the dusky phenotype. You look up dusky in FlyBase, the online database of Drosophila genetics and genomics, and learn that, in wildtype flies, the dusky gene is contained within an 8-kb Xho I restriction fragment. When you digest genomic DNA from the mutant male with Xho I and probe with the 8-kb restriction fragment on a Southern blot, you find that the size of the labeled fragment is 10 kb. You clone the 10-kb fragment and use it as a probe for in situ hybridization with the polytene chromosomes of a number of different wildtype strains. You notice that this fragment hybridizes to multiple locations along the polytene chromosomes. Each wildtype strain has a different pattern of hybridization. What do these data suggest about the origin of the dusky mutation that you discovered?