What have we learned from sequencing animal genomes?

In certain dog breeds, such as whippets, the muscles of some individuals can be much bulkier than is normal. Genome analyses have shown that the gene for myostatin, a protein that inhibits muscle growth, is mutated in whippets that have bulky muscles. When the myostatin gene is mutated, the protein that inhibits muscle growth is dysfunctional (Figure 17.16). Comparative genomics reveals that the myostatin gene is also mutated in certain breeds of cattle and sheep that are noted for overdeveloped muscles.

With the knowledge that myostatin affects muscle development, some consideration has been given to the possibility of manipulating myostatin in humans to treat muscle-wasting diseases such as muscular dystrophy. As you might expect, athletes anxious to have bulkier muscles are also very interested in this gene and its protein product.

Future directions

Few scientific endeavors have received as much hype and hope as genome sequencing. A major effort is under way to sequence the genomes of tumors in as many people as possible, to screen for mutations. When the BRCA1 gene was identified as mutated in breast cancer (see Chapter 15), some medical scientists hoped that cancer would be like other genetic diseases such as sickle-cell anemia—caused by a single mutation in a single gene. So far, the lessons learned from cancer genomes include that there are many mutations in a tumor, and that some of them drive the tumor formation while others do not; that the mutations in one person’s tumor of a particular type may differ from those in the same tumor in someone else; and that tumor genomes evolve over time as the tumor grows and spreads. Understanding tumor genomes is not straightforward. Nevertheless, the goal is to study genomes to determine how gene products and the environment interact to form the tumor phenotype, and to design therapy for that tumor in individual people. This is called precision medicine, and it is in the future. It is a model for a goal of genomics: to determine the relationship between genotype, the environment, and phenotype.