Each person’s cancer has a unique combination of genetic changes. As the cancer continues to grow, additional changes will occur. Even within the same tumor, different cells may have different genetic changes.

Although the immune system normally removes damaged or abnormal cells from the body, some cancer cells are able to “hide” from the immune system.

For example, Sarah's work supports the hypothesis that lighter skin in climates further away from the sun gave an individual a selective advantage (because their skin was able to make more vitamin D and avoid diseases like rickets). In contrast, darker skin color was helpful in climates with more sun (because the pigments in the skin help to prevent sun damage and skin cancer).

In fact, at least ten genes each of which comes in several "flavors," contribute to eye color. It is the combination of these gene variants in a person's genome that produces the wonderful range of human eye colors.

Forensic testing is carried out for legal purposes and can be used to identify biological family members, suspects, and victims of crimes and disasters.

Nearly all humans have the same genes arranged in roughly the same order and more than 99.9% of your DNA sequence is identical to any other human. Still, we are different. On average, a human gene will have 1-3 letters that differ from person to person. These differences are enough to change the shape and function of a protein, how much protein is made, when it's made, or where it's made. They affect the color of your eyes, hair, and skin. More importantly, variations in your genome also influence your risk of developing diseases and your responses to medications.

he chromosomes of prokaryotes aremuch simpler than those of eukaryotes in many of their features (Figure 9.6). Most prokaryotes contain a single, circularchromosome that is found in an area in the cytoplasm called the nucleoid.

Eukaryotes, whose chromosomes each consist of a linear DNA molecule, employ a different type of packing strategy to fittheir DNA inside the nucleus (Figure 9.7). At the most basic level, DNA is wrapped around proteins known as histonesto form structures called nucleosomes. The DNA is wrapped tightly around the histone core. This nucleosome is linked tothe next one by a short strand of DNA that is free of histones. This is also known as the “beads on a string” structure; thenucleosomes are the “beads” and the short lengths of DNA between them are the “string.”

The latter half of the twentieth century began with the discovery of the structure of DNA, then progressed to thedevelopment of the basic tools used to study and manipulate DNA. These advances, as well as advances in ourunderstanding of and ability to manipulate cells, have led some to refer to the twenty-first century as the biotechnologycentury. The rate of discovery and of the development of new applications in medicine, agriculture, and energy is expectedto accelerate, bringing huge benefits to humankind and perhaps also significant risks. Many of these developments areexpected to raise significant ethical and social questions that human societies have not yet had to consider.

To study or manipulate nucleic acids, the DNA must first be extracted from cells. Various techniques are used to extractdifferent types of DNA (Figure 10.2). Most nucleic acid extraction techniques involve steps to break open the cell, and thenthe use of enzymatic reactions to destroy all undesired macromolecules. Cells are broken open using a detergent solutioncontaining buffering compounds. To prevent degradation and contamination, macromolecules such as proteins and RNAare inactivated using enzymes. The DNA is then brought out of solution using alcohol. The resulting DNA, because it ismade up of long polymers, forms a gelatinous mass.

Many brains are observed while people are doing a task. The partof the brain that lights up, indicating activity, is then demonstrated to be the part controlling the response to that task.