Chapter 10, Problem 9EQ

In Chapter 23, the technique of fluorescence in situ hybridization (FISH) is described. This is another method for examining sequence complexity within a genome. In this method, a DNA sequence, such as a particular gene sequence, can be detected within an intact chromosome by using a DNA probe that is complementary to the sequence. For example, let’s consider the $\text{β-globin}$ gene, which is found on human chromosome 11. A probe complementary to the $\text{β-globin}$ gene binds to that gene and shows up as a brightly colored spot on human chromosome 11. In this way, researchers can detect where the $\text{β-globin}$ gene is located within a set of chromosomes. Because the $\text{β-globin}$ gene is unique and because human cells are diploid (i.e., have two copies of each chromosome), a FISH experiment shows two bright spots per cell; the probe binds to each copy of chromosome 11. What would you expect to see if you used the following types of probes?

A. A probe complementary to the Alu sequence

B. A probe complementary to a tandem array near the centromere of the X chromosome