There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer starts in cells of the lung, and brain cancer starts in cells of the brain

They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun. (Our Cancer Causes and Prevention section has more information.)

Another area where our understanding of biology has greatly advanced is in the genomics of skin color. Unfortunately, for centuries, skin color has been used as the basis for discrimination against some populations, a consequence of the inaccurate concept of human races.

In fact, at least ten genes each of which comes in several "flavors," contribute to eye color.

In fact, each species of plants and animals has a set number of chromosomes. A fruit fly, for example, has four pairs of chromosomes, while a rice plant has 12 and a dog, 39.

So, mitochondrial DNA is always inherited from the female parent. In humans, a few conditions, including some forms of hearing impairment and diabetes, have been associated with DNA found in the mitochondria.

Pharmacogenomic testing tells you about how you will react to certain medications. It can help inform your healthcare provider about how to best treat your condition and avoid side effects.

just one letter missing or changed may result in a damaged protein, extra protein, or no protein at all, with serious consequences for our health. Additionally, the passing of genetic variants from one generation to the next helps to explain why many diseases run in families, such as in sickle cell disease, cystic fibrosis, and Tay-Sachs disease.

A gene is a segment of DNA that provides the cell with instructions for making a specific protein, which then carries out a particular function in your body.

DNA analysis often requires focusing on one or more specific regions of the genome. It also frequently involves situationsin which only one or a few copies of a DNA molecule are available for further analysis. T

Dolly the sheep was the first agricultural animal to be cloned.

With the exception of identical twins, each person’s DNAis unique and it is possible to detect differences between human beings on the basis of their unique DNA sequence

forms a double stranded helix, and

Also, the development of molecular techniques and the establishment of DNAdatabases have updated the types of work that forensic scientists can do.

Figure 1.18The scientific method is a series of defined steps that include experiments and careful observation. Ifa hypothesis is not supported by data, a new hypothesis can be proposed.In the example below, the scientific method is used to solve an everyday problem. Which part in the examplebelow is the hypothesis? Which is the prediction? Based on the results of the experiment, is the hypothesissupported? If it is not supported, propose some alternative hypotheses.1. My toaster doesn’t toast my bread.2. Why doesn’t my toaster work?3. There is something wrong with the electrical outlet.4. If something is wrong with the outlet, my coffeemaker also won’t work when plugged into it.5. I plug my coffeemaker into the outlet.6. My coffeemaker works

Ahypothesisis a suggested explanation for an event, which can be tested.

Figure 1.14Formerly called blue-green algae, the (a) cyanobacteria seen through a light microscope are some ofEarth’s oldest life forms. These (b) stromatolites along the shores of Lake Thetis in Western Australia are ancientstructures formed by the layering of cyanobacteria in shallow waters. (credit a: modification of work by NASA; scale-bar data from Matt Russell; credit b: modification of work by Ruth Ellison)Like geology, physics, and chemistry, biology is a science that gathers knowledge about the natural world. Specifically,biology is the study of life. The discoveries of biology are made by a community of researchers who work individuallyand together using agreed-on methods. In this sense, biology, like all sciences is a social enterprise like politics or the arts.The methods of science include careful observation, record keeping, logical and mathematical reasoning, experimentation,and submitting conclusions to the scrutiny of others. Science also requires considerable imagination and creativity; awell-designed experiment is commonly described as elegant, or beautiful. Like politics, science has considerable practicalimplications and some science is dedicated to practical applications, such as the prevention of disease (seeFigure 1.15).Other science proceeds largely motivated by curiosity. Whatever its goal, there is no doubt that science, including biology,has transformed human existence and will continue to do so.Figure 1.15Biologists may choose to studyEscherichia coli(E. coli), a bacterium that is a normal resident of ourdigestive tracts but which is also sometimes responsible for disease outbreaks.