Like a genome, a textbook evolves. This sixth edition has undergone a few insertions, deletions, and rearrangements.

Emphasis on control of gene expression.

• Chapter 10 has undergone binary fission: It now focuses on “Gene Action.’
• Chapter 11 presents “Control of Gene Expression.” This new chapter explores gene expression through time and tissue; chromatin remodeling via the histone code and RNA interference; and the enigma of a genome that devotes only 1.5 percent of its information to encoding proteins, and the fact that those proteins greatly outnumber the genes that specify them.
• The theme of gene expression continues in a practical sense in chapter 18, “The Genetics of Cancer.” Figure 18.2 presents data that have saved lives—DNA microarrays that revealed why some people with a rare form of leukemia do not survive given standard treatments for the more common form; they have a different illness, apparent only at the level of gene expression.

Unparalleled coverage of stem cell biology.

• To accompany chapter 2’s (“Cells”) clear descriptions, four illustrations progress from basic to applied views of stem cells. Unlike most textbook depictions, figures 2.22 and 2.23 show stem cells giving rise to other stem cells, as well as daughter cells that go on to yield differentiated cells. Figure 2.24 takes the reader through the steps of somatic cell nuclear transfer, and figure 2.25 looks at stem cells from adults to heal a young man’s heart.
• The stem cell theme continues in figure 11.4, which depicts how differential gene expression guides development of the pancreas into a uniquely dual structure—from a single type of progenitor cell.

Classical genetic observations viewed from a genomic perspective.

• Redundancy in gene function sheds new light on chapter 5’s “Extensions and Exceptions to Mendel’s Laws,” a group of important topics ignored in some other books.
• In chapter 7, “Multifactorial Traits,” eye color is no longer considered a simple blue or brown, but includes the specks and flecks, shading and intensity that arise from the landscape at the back of the eye, providing great variability. Figure 7.12 summarizes the gene-controlled hormonal interactions that regulate body weight, also a phenotype not as simple as we once thought.

Updated examples.

• Chapter 15, “Changing Allele Frequencies,” discusses the emerging infectious diseases SARS and West Nile virus illness. Discussion of the possible effect of long-ago cannibalism on resistance to prion diseases fleshes out the coverage of balancing selection.
• New topics in Chapter 16, “Human Origins and Evolution,” include targeted comparative sequencing to track shared ancestries; the 160,000-year-old H. sapiens idaltu, who looked amazingly like us; and a consideration of the many clues pointing to a duplication of the entire human genome.
• New “stories” integrated into the narrative include:
  Callipyge sheep, whose giant rears illustrate genomic imprinting (chapter 6, “Matters of Sex”)
  Let sleeping dogs lie: how dogs with narcolepsy led to discovery of the gene in humans (chapter 8, “The Genetics of Behavior”)
  Rosalind Franklin’s famed “photo 51” (chapter 9, “DNA Structure and Replication”)
  The “blue people of Troublesome Creek” (chapter 12, “Gene Mutation”).

Capstone.

• Chapter 22, “The Age of Genomics,” has translocated material to earlier chapters, and has deleted descriptions of techniques no longer used, yet it preserves the telling of the historic race to sequence the human genome. New topics include “$1000 genome” sequencing technologies; the National Human Genome Research Institute’s three-tiered architectural metaphor for the future of genomics; studies that focus on the healthy, rather than those with rare disorders; and a better understanding of the roots of disease. New genetic knowledge is not only providing information for the development of new diagnostic tests and treatments, but is easing identification of non-genetic factors that compromise health.

New Boxes

• The cast of real characters who have shared their experiences in past editions in “In Their Own Words” boxes update their stories, and are joined by some new voices.
• In “The Y Wars” (chapter 6), researcher Jennifer Marshall-Graves laments “The Rise and Fall of the Human Y Chromosome,” while David Page describes “Rethinking the Rotting Y Chromosome.”
• On a more serious note, parents tell the sad but inspiring tales of their children who have familial dysautonomia (chapter 12) and Li-Fraumeni family cancer syndrome (chapter 18, “The Genetics of Cancer”).

New Design, New Tables, and New Figures Throughout

• A bright, modern, bold design sets the stage for the fascinating topic of genetics.
• Tables present the main points to ease studying.
• New figures add historical depth, highlight genomic approaches to traditional ideas, introduce technology, present news, and even offer artists’ renditions of genetics.