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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 14. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. Is it possible that the legendary single-eyed Greek adversary “Cyclops” actually existed?
  2. In terms of total number of base pairs, which organisms have the largest genome?
  3. What are transposons?  Where did they come from and how much of the human genome is comprised of transposons?
  4. If the total amount of DNA present in your body were to be stretched end-to-end, how long would these molecules measure and how does this compare to the distance between the sun and Earth?
  5. How many different types of cells are present in the human body?  How many of these types produce the protein hemoglobin?
  6. What are “housekeeping” genes?
  7. In terms of homeotic genes, how are humans similar to fruit flies?
  8. In the bacteria E. coli, how is the production of the amino acid tryptophan regulated?
  9. What is a “DNA Chip” and how can it be used in the diagnosis of disease?

A Guide to the Reading

When exploring the content in Chapter 14 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.


The human genome consists of approximately 3.3 billion base pairs containing roughly 25,000 genes.  It is estimated that only 1.5 percent of the genome contains information encoding a protein.  In addition to non-coding and spacer DNA sequences, a typical eukaryotic genome also contains a large number of transposons.  Transposons are sequences of DNA which are capable of changing their position within the genome.  As such, they are often referred to as “jumping genes”.  As discussed in the text, it is estimated that upwards of 36 percent of the human genome is made up of transposons.  Scientists believe that transposons likely originated from a viral source.  How do these jumping genes change position within the genome?  In many cases, the gene sequence present in the transposon codes for an enzyme which facilitates the removal of the transposon from its original location and subsequent insertion in its new location.  Recall from Chapter 12 that specialized enzymes used in the repair of DNA are capable of performing these same removal and insertion functions.

For more information on this concept, be sure to focus on:

  • In Section 14.1, Genes constitute only a small percentage of the DNA in eukaryotes
  • Figure 14.3, The Composition of Eukaryotic DNA
  • Table 14.1, Types of Eukaryotic DNA

Differential Gene Expression

Humans have more than 200 different types of cells.  As discussed in Chapter 11, each of these cells, regardless of type, contain the exact same set of genes.  So how does the body produce over 200 different cell types even though the DNA present within each cell type is exactly the same?  This is accomplished through the selective expression of a subset of genes required for each particular cell type.  For example, skin and hair cells produce a strong, fibrous protein called keratin that allows these cells to perform their protective function.  As mentioned in the chapter, red blood cells in the body are the exclusive producers of the oxygen-transporting protein hemoglobin.  Examples such as these illustrate how cells become specialized depending upon the subset of genes that they express.  In addition to this differential gene expression, a subset of genes called “housekeeping genes”, are expressed in almost all cells in the body.  These genes code for universally required products such as different types of RNA. 

For more information on this concept, be sure to focus on:

  • In Section 14.3, Different cells in eukaryotes express different genes
  • Figure 14.6, Different Types of Cells Express Different Genes

Controlling Gene Expression

As discussed in the chapter, the cell uses several distinct methods for controlling the expression of genes.  The primary mechanism utilized by most cells, however, is by controlling the process of transcription.  Regulatory DNA sequences may be used by the cell to either promote or inhibit the transcription of particular genes.  Inhibition of the expression of a gene sequence can be accomplished through the binding of a repressor protein, such as that used by the tryptophan operator discussed in the chapter, to the regulatory sequence.  The presence of the repressor protein can then block the binding of RNA polymerase and subsequently inhibit the process of transcription.  Conversely, promoter proteins which promote the attachment of RNA polymerase may bind to regulatory sequences which results in the enhanced transcription of the genes.  To add more complexity to the process of gene regulation, it is important to understand that the activity of these promoter or repressor proteins may be turned on or off depending upon cellular or environmental conditions.  Therefore, the regulation of gene expression can be thought of as an elegantly complex cascade of events that work together to make the production of proteins a highly efficient process.

For more information on this concept, be sure to focus on:

  • In Section 14.4, Cells control the expression of most genes by controlling transcription
  • In Section 14.4, Cells also control gene expression in other ways
  • Figure14.9, Repressor Proteins Turn Genes Off
  • Figure 14.10, Control of Gene Expression in Eukaryotes

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

Environmental Influence on Gene Expression (Phenotype)

  • Chapter 10 – in Section 10.5, The environment can alter the effects of a gene


  • Chapter 11 – Section 11.1, The Role of Chromosomes in Inheritance

One Gene – One Protein (or RNA molecule)

  • Chapter 13 – Section 13.1, Genes Encode Proteins

The Role of Genes in Development

  • Chapter 29, Reproduction and Development

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