Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 18

In Chapter 8, Figure 8.7 describes the evolution of the globin gene family. All genes in this family are homologous to each other, though the degree of sequence similarity varies depending on the time of divergence. Genes that have diverged more recently have sequences that are more similar. For example, the 1 and 2 genes have DNA sequences that are more similar to each other than to the 1 and genes. In a Southern blotting experiment, the degree of sequence similarity can be discerned by varying the stringency of hybridization. At high temperature (i.e., high stringency), the probe recognizes genes that are only a perfect or very close match. At a lower temperature, however, homologous genes with lower degrees of similarities can be detected because slight mismatches are tolerated. If a Southern blot was conducted on a sample of human chromosomal DNA and a probe was used that was a perfect match to the -globin gene, rank the following genes (from those that are detected at high stringency down to those that are only detected at low stringency) as they would appear in a Southern blot experiment: Mb , 1 , , A , , and .FIGURE 8.7 The evolution of the globin gene family in humans. The globin gene family evolved from a single ancestral globin gene. The first gene duplication produced two genes, one that encodes myoglobin (on chromosome 22) and a primordial hemoglobin gene that duplicated several times to produce several -chain and -chain genes, which are found on chromosomes 16 and 11, respectively. The four genes shown in gray are nonfunctional pseudogenes.