In a 4- to 5-page Microsoft Word document, create a work sheet by answering the Questions for Research and Discussion provided for each case study. (Do not answer the multiple-choice questions).

Cite any sources in APA format.

Learning Outcomes

9.1   Experiments Identify and Describe the Genetic Material

  1. Describe the experiments that showed that DNA is the genetic material and protein is not.
  1. Explain how Watson and Crick deduced the structure of DNA.

9.2   DNA Structure

  1. List the components of a DNA nucleotide building block.
  1. Explain how nucleotides are joined into two chains to form the strands of a DNA molecule.

9.3   DNA Replication—Maintaining Genetic Information

  1. Explain the semiconservative mechanism of DNA replication.
  1. List the steps of DNA replication.
  1. Explain how the polymerase chain reaction amplifies DNA outside cells.

9.4   Sequencing DNA

  1. Explain the basic strategy used to determine the base sequence of a DNA molecule.
  1. Explain how next-generation sequencing improves upon Sanger sequencing.

image The BIG Picture

DNA is the basis of life because of three qualities: It holds information, it copies itself, and it changes.

On the Meaning of Gene

To a biologist, gene has a specific definition—a sequence of DNA that tells a cell how to assemble amino acids into a particular protein. To others, “gene” has different meanings:

To folksinger Arlo Guthrie, gene means aging without signs of the Huntington disease that claimed his father, legendary folksinger Woody Guthrie.

To rare cats in New England, gene means extra toes.

To Adolph Hitler and others who have dehumanized those not like themselves, the concept of gene was abused to justify genocide.

To a smoker, a gene may mean lung cancer develops.

To a redhead in a family of brunettes, gene means an attractive variant.

To a woman whose mother and sisters had breast cancer, gene means escape from their fate—and survivor guilt.

To a lucky few, gene means a mutation that locks HIV out of their cells.

To people with diabetes, gene means safer insulin.

To a forensic entomologist, gene means a clue in the guts of maggots devouring a corpse.

To scientists-turned-entrepreneurs, gene means money.

Collectively, our genes mean that we are very much more alike than different from one another.

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9.1 Experiments Identify and Describe the Genetic Material

“A genetic material must carry out two jobs: duplicate itself and control the development of the rest of the cell in a specific way,” wrote Francis Crick, codiscoverer with James Watson of the three-dimensional structure of DNA in 1953. Only DNA fulfills these requirements.

DNA was first described in the mid-nineteenth century, when Swiss physician and biochemist Friedrich Miescher isolated nuclei from white blood cells in pus on soiled bandages. He discovered in the nuclei, an unusual acidic substance containing nitrogen and phosphorus. He and others found it in cells from a variety of sources. Because the material resided in cell nuclei, Miescher called it nuclein in an 1871 paper; subsequently, it was called a nucleic acid. Few people appreciated the importance of Miescher’s discovery at the time, when inherited disease was widely blamed on protein.

In 1902, English physician Archibald Garrod was the first to provide evidence linking inherited disease and protein. He noted that people who had certain inborn errors of metabolism lacked certain enzymes. Other researchers added evidence of a link between heredity and enzymes from other species, such as fruit flies with unusual eye colors and bread molds with nutritional deficiencies. Both organisms had absent or malfunctioning specific enzymes. As researchers wondered about the connec

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